Where you can get into trouble is if the problem affects all your instances across the entire cluster. If all your organization's code is running in the same process, if any of that code has a severe memory leak or other serious issue, it could impact the stability of everything else.

Not to say that wouldn't happen for SPOF microservices (e.g. your auth servers), but the surface area is potentially larger for monoliths.

On the other hand, if a memory leak concerns one key microservice your whole operation is also likely to suffer, even if 99% of services run fine.