Crimping multiple wires to a single crimp

First let me say that at one point it was my full-time job to design cable harnesses and documentation for these, and to outsource the production to sub-contractors who specialized in manufacturing cable-harnesses.

Is this the recommended approach? If not, what would you advice?

No it is definitely not the approach I would recommend

If you pair multiple wires in one crimp terminal then you can no longer trust the holding-force specification of the crimp, nor can you be sure of the crimping resistance or current rating if you do that..

Crimp terminals might seem like a simple/primitive technology, but in reality good quality crimp terminals are meticulously designed to work with a specific type and gauge of wire.

Should I be aware of any reliability issues? Can these be controlled or mitigated?

Yes if you choose to combine multiple wires into one crimp then you absolutely need to be wary of reliability issues. And no they can not be mitigated if you use this approach, in fact I can promise you that you will have reliability issues.

The approach I prefer, and the approach that the sub-contractors I have used also preferred, is to use a solder-connector instead of a crimp connector, and solder three wires unto the same terminal, rather than trying to crimp a terminal around three wires.