- Do you use proxy attributes in your rig? (tl;dr: don’t!)
- If removing proxy attributes doesn’t work, you said you were using Maya 2019. This version was trash in my experience. I recommend testing in 2020.4 to see if it opens, just to isolate if it is a 2019 problem or not.)
- Have you seen this thread? Maya 2020.2 crash when opening rig
And especially if both #1 and #2, I seem to remember there was specifically a bug in Maya 2019 related to proxy attributes. So you can either try building without them, or upgrade Maya. In either case, I highly recommend removing proxy attributes. They also mess up the graph editor.
The only benefit to proxy attributes is a slight convenience of having attributes like the ik/fk switch on multiple controls.
(While taking that above screenshot, I was horrified to learn I had accidentally been building my rigs with proxy attributes on a current project.)