ERROR:

The class "N3abm10RollUpAcctE" in the model file has changed
size from 432 to 456 bytes and cannot be updated while opening
a model. Please upgrade the model file using the backup and
restore utility

https://support.sas.com/documentation/onlinedoc/abm/8.42/install.pdf Page 10
download it from here if the original has gone

SOLUTION

If you see this error, take the following steps:
1. Stop the SAS Object Spawner.
2. Navigate to the Models directory path, which is typically
SASConfig/Lev1/SASApp/ABMServer/Models on the compute tier.
3. Rename the M0 folder to M0_rename.
4. Start SAS Object Spawner.
5. Log back in to the client.

You're welcome :)
20240824

And many thanks to Karl!