When is the word rate used in the plural?

To evaluate the transmission rate of the LRU channel,we evaluate it as
a covert channel using one target set.

When d = {2, 4, 6}, the error rate is large on E5-2690.

Figure 5 (top) shows the error rate of the channel versus the
different transmission rates

Detailed analysis and evaluation of the LRU channels, including
evaluation of the transmission rates and bit error rates of the LRU
covert channels on both Intel and AMD processors and comparison of the
LRU channels with the existing cache channels from the perspective of
encoding time and cache miss rates.

The rate in the last sentence is plural. Why not use a plural number for the previous rate? Especially in the second sentence, it clearly refers to not one. Including words such as channel makes me very confused. Sometimes they use plurals, sometimes not? Is there any way to judge?
These rates all refer to the results on a graph.
Thanks!