Game fatal error after upgrade to 5.03

Hello,

After upgrading a c++/Blueprint project from UE 4.26 to UE 5.03, everything seems to be working in Editor. Even the packaging works with no trouble (just a few error messages that never made any difference), but once launching the game, I have a Fatal Error crash with this log:

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x0000000000000290

0x00007ff7074b239b MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff70539c75a MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff70539fb68 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff7053a7559 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff705397a86 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff7054a8a24 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff7054a88da MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff707849583 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff707832a32 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff707853f70 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff707398443 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff7048693a4 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff70487223c MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff7048722ba MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff704873554 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff70487bf74 MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ff7081ee7be MyProject-Win64-Shipping.exe!UnknownFunction []
0x00007ffeba557034 KERNEL32.DLL!UnknownFunction []
0x00007ffebc2c2651 ntdll.dll!UnknownFunction []

Does anyone have an idea where this could come from or how I could swim up to the source ? I updated the graphics card, added a HKEY_LOCAL_MACHINE DWORD (TdrDelay), tried removing big chunks of the code to find a potential suspect, but it keeps crashing.

Thanks for your help.