Clarity when it comes to active and passive voice

A bug is defined as a problem causing issues in production.

Active voice: A problem causing issues in production defines a bug.

Your translation into active voice is incorrect. A problem with the passive is that we needn't specify the agent. To change to the active, we must supply one because that will be the subject of the new sentence.

Ask yourself, Who defines a bug in this way?

We could have

1. A bug is defined (by the company) as a problem causing issues in production.

2. A bug is defined (by my dictionary) as a problem causing issues in production.

3. A bug is defined (by most people) as a problem causing issues in production.

In case (1), the active version would be

The company defines a bug as a problem causing issues in production.

---

Having said that, I see no problem with using the passive for lists or dictionary entries. Ignore Grammarly - the keyword needs to come first and you can state who is doing the defining in the introduction to the list.

You could avoid the problem of passive voice altogether by removing the portion that introduces it.

A bug is defined as a problem causing issues in production.

Even better,

A bug is a problem that causes issues in production.

Passive voice is not an error. Sometimes the passive voice sentence is clearer or allows a writer to emphasize what they want.

Many educators and resources do tell students to write in active voice for stylistic reasons. For example, Richard Lanham in his book Revising Prose poses a sentence-level editing method called the Paramedic Method that involves revising most sentences so that they have simple active verbs. Lanham wants to see more writers embrace a clear style unburdened by stilted, circuitous constructions. While Lanham spends the last part of his first chapter admitting that "rules don't always work and exceptions exist, if not to disprove the rules, then to encourage common sense in applying them" (p. 18), adaptations of his method often go all-in on changing passive voice to active voice. Purdue OWL claims:

The Paramedic Method also helps you activate your sentences by eliminating passive voice and redundancies.

The University of Richmond Writing center advises that students always write active sentences:

Replace as many "to be" verbs with action verbs as you can, and change all passive voice ("is defended by") to an active voice ("defends"). [...] If you get stuck in a passive sentence always ask the question: "Who does what to whom?" If you use that formula you will always write active sentences.

This attitude is common among educators.

However, many people also defend the use of passive voice in specific disciplines or situations. For example, STEM writing requires the use of passive voice in situations where the person performing an action is relatively unimportant. While one of Angelika H. Hofmann's guidelines for scientist-writers in Scientific Writing and Communication is to "Use active voice," she follows that up with caveats (p. 49):

Do not remove the passive voice completely, however; use the passive voice when readers do not need to know who performed the action (such as in the Materials and Methods section; see Chapter 11, Section 11.4). You may also have to use the passive voice when the emphasis should be on a specific topic or when word location needs to be considered [...]

In addition, you should use the passive voice if this allows you to replace a long subject with a short one, gives you a more consistent point of view (i.e., lets you use the same subject in consecutive sentences), or lets you put emphasis on the terms you want to have emphasized.

Hofmann's list is excellent, and can be used to assess your own examples as well as an alternative active voice revision (Active voice 2) I'll pose for you.

Passive voice: A bug is defined as a problem causing issues in production.

Active voice 1: A problem causing issues in production defines a bug.

Active voice 2: I define a bug as a problem causing issues in production.

The passive voice construction emphasizes a bug. That short subject is obviously preferable to the first active voice example, which has a much less concise subject ("A problem causing issues in production"). The passive allows us to replace a long subject with a short one.

That said, what about the second active voice example, with its short subject ("I")? Now it's a question of emphasis - would you rather emphasize the agent, the one who poses the definition? Use "I" and active voice. Is this definition uncontroversial, and is your purpose primarily informative? Use "A bug" and passive voice.

In other words, choosing active and passive voice here is a question of what you want to emphasize.

Firstly, the clarity of one's writing isn't dependent on whether their writing is packed with active or passive sentences. The impact, however, sure is.

NeuroSummer was given an ice cream (by NeuroWinter.)

The above sentence may be passive, but if the narrative focus is on NeuroSummer, then it'll be a perfect choice.

NeuroWinter gave NeuroSummer an ice cream.

NeuroWinter gave ice cream to NeuroSummer.

These two sentences are in the active voice, but it has the following focus order: NeuroWinter>> NeuroSummer === Ice cream.

So passive voice, at times, can have a much greater impact than its corresponding active voice. That said, you must avoid passive sentences as much as possible during situations like fight scenes where the pacing is crucial and the tension is high. One or two passive sentences in a scene such as 'NeuroFall was chased by a reindeer' will work just fine, but it's better to use them sparingly.

Now, moving on to the main part...

To simply define Active and Passive voices, the subject is active in the former, and passive in the latter.

NeuroSpring was chased by a polar bear(one that just left hibernation, of course). ---> the subject here is receiving the action.

A polar bear chased NeuroSpring. --> the subject here is doing the action.

But note that the subject is always the MAIN focus. (That's how our subconscious minds' perceive it, I think)

If both voices do their jobs, why only passive sentences get the short end of the stick?

Rani's skull was broken to pieces by Raja. ---> Passive, so tends to be wordy.

Raja shattered Rani's skull ---> Active, tends to be concise, and also allows you to use stronger, vivid verbs.

More examples...

Sparrows could be seen flying in the sky.

Sparrows fluttered about in the sky.

Sheela was a lovely girl. She was liked by everyone so much.

Everyone likes a lovely girl like Sheela.

If you want Sheela to be in focus and be better in the passive voice, then...

A lovely girl like Sheela was liked by everyone so much.

Last but not least, there are many ways to write one sentence, but choose the one that best fits your scene, regardless of its voice.