@CarlFrischmuth Thanks for posting and I'm sorry to here about these issues. So far, I don't believe I've run across anyone else reporting the same issues you are reporting.
Does this issue seem to be related to one specific design? Feel free to share it with me if you would like me to take a closer look. I am happy to see if I can help. You can private message me a share link if you prefer to keep it private.
I suspect that the issue with the Material change may have caused a recompute of some features that may have already had errors in them. If performing a compute on a feature causes it to fail repeatedly, it would be really helpful to document exactly what is happening.
Are your timelines typically clean of error messages and warnings when you perform a Compute All (CTRL + B or Command + B)? How often do you perform a Compute All to verify that your Timeline is free of errors and warnings? I would definitely recommend using this before saving a design. It will help to flush out errors.
Restructuring the Timeline can be very tricky and managing all of the relationships in a design can be complicated. One tip is to use distributed designs to keep the timelines in your designs clean, short, simple and healthy. In the design in question, how long is the Timeline?
Another approach is to simply ditch the parametric approach. Just because it is there, it doesn't mean you must use it! I'm not sure about the end goal here; however, I'm wondering if you really need to have a parametric design? Could you work with a Direct Modeling design instead? I note also that you can right click on features in the timeline and convert them to DM features.
I hope this information is helpful. I look forward to your reply. Please let me know if there are any questions or if there is anything I can do to help.
Kind regards,.
Nathan Chandler
Principal Specialist