The reason I never searched for code review software is because I rarely have issues with it.
The biggest problem was when reviews took a while because people forgot to check MRs for replies if the MR wasn’t assigned to them. So we built a bot to ping them in slack and/or assign the MR to the person that needs to reply.
If the MR is to big we close the MR, and the initial dev has to split the changes up into multiple MRs.
Etc.
I’d say 99% of issues with code review is everyone not being on the same page about how MRs should be done, but once we sync on that, issues are scarce.