I don’t know if this is an issue or not. When updating projects directly from Unity 2018 to 2020, the Glyph IDs in Sprite Assets all get set to zero (see attached). Simple enough to fix (once I noticed it was happening).
What version of the TMP package were you using in 2018.4?
What version did you upgrade to in 2020.x?
Can you provide me with the working sprite asset in 2018.4?
I would like to take a look to see if I can spot why these values didn’t translate correctly. It is possible that you went from a new version of the TMP package in 2018.4 to an older default version of the TMP package in 2020 which would have the potential of messing something up.
The projects (there were a few) started in Unity 2018.2.21f1, TMP version 1.2.3. I updated them to Unity 2020.3.11f1. I don’t see a version number in the 2020 TMP settings panel. I see ## [3.0.6] - 2021-04-23 in the change log, is that the version? I assumed updating the project to 2020 also updated TMP, I didn’t reimport it.
It won’t let me upload an asset file.
I recently updated some other projects from 2018, but I updated those to 2019 first because some textures were getting mixed up if I went straight to 2020. Sprite assets came through OK in those projects.
Version 1.2.3 is “old” and would most certainly be using the old format for sprite assets.
Best way to provide me with one of those assets would be to export it and then zip it. The forum should allow you to post a zip file.
If the asset is sensitive, you can always provide me with this via private message or some private link.
Attached is a Zip with the asset from a 2018 project that had a problem after updating.
7456067–915029–Figures Atlas.zip (355 KB)