I have the same problem (corona 5 3ds max 2021) only corona 3 works fine.
Please solve bugs quikly!!!!
Everybody is having this bug since Corona 3 as far as I know. If anyone does not , I would like to know .
This also seems like insanely hard to fix since it takes so long. I cannot fathom why but I trust Corona team that its hard. Those bugs are not intuitive in their complexity to solve.
I don't really understand why people expect merging to be a trivial thing in 3ds max, let alone Corona to handle it. Max has a notoriously hyperactive notification system that runs all the time and sends info forth and back all the time and is triggered almost all the time without a reason. It includes all areas when merging - file i/o, geometry, modifiers, lights, controllers, animation and keyframes, materials and maps, even the UI seems to be involved. Expecting Corona to run smoothly while merging and perform perfectly is maybe too much.
Also, there are minor changes between each version of Max. Something that worked in 2016 won't work in 2019 or 2020, and it's perfectly possible that the Corona team is not even aware of these changes because some of them may be undocumented. Or there could be bugs that no one knows about yet, why would you expect the Corona team to work around stuff when they just can't? They will probably never be able to catch up, and it may not be within their power anyway.
Please guys, stop expecting the impossible and just accept that stopping the IR by yourself prior to merging is probably the most reasonable thing to do. It's not that much of an inconvenience, is it? Let the team focus on other things instead.