I upgraded CC3 and subsequently started having problems with characters created under UE4 version 4.25.3. The character is regularly exported to fbx and imported under UE4, when I try to do any operation with the characters exported after updating CC3 I get the following error in UE4 and UE4 resets:Assertion failed: AllocationId> = 0 && AllocationId <= 255 [File: D: / Build / ++ UE4 + Licensee / Sync / Engine / Source / Runtime / Engine / Private / Materials / MaterialInterface.cpp] [Line: 611].All characters imported with the outdated version of CC3 work smoothly. Unfortunately the imported characters after the update crash the UE4 program just by clicking on it.

Hello emypippo, did you mean it only happens after upgrading to CC v3.22?

Exact. After updating the CC3 I converted the old characters with the new CC3 and then I exported and imported them to UE4. Unfortunately, the new characters crash the UE4 system, unlike the old ones.

That's too bad!
May you help to submit this issue to Feedback Tracker, and paste forum link as reference?
We may need your help to provide project to easily duplicate this issue. 

Once it's submit on Feedback Tracker, I will help to highlight this issue to Dev Team. Thank you!

Volentieri. Potreste inviarmi il link per il Feedback Tracker?

Gladly. Could you send me the link for the Feedback Tracker?

Hello, here you go. (login required)
https://www.reallusion.com/FeedBackTracker/

Many thanks!

I posted as you indicated.
https://www.reallusion.com/FeedBackTracker/Issue/UE4-Crash-with-imported-character

Thank you!