Hey efosGD,
If the problem is occurring solely in this specific project, it could be the project and contents within have been corrupted. This can happen when you migrate content that is tied specifically to a project and its engine version. You mentioned you had been working on a project for a while, which I can assume you upgraded the engine version at least once?
If you used the ‘Convert-in-Place’ option instead of the ‘Open a Copy’ option when upgrading your project’s engine version, this could be the culprit. I always suggest opening a copy instead of converting in place for compatibility reasons. This will ensure your original project does not get corrupted in the upgrading process.
Unless I can reproduce this issue on my end, which seems unlikely, this is a project specific issue. Moving forward, try to be careful about migrating assets between engine versions and projects. Always take the safer route and create a copy before taking any actions.
Thank you,