Dorico 4.3 Crashes when opening & editing project from Dorico 3.5

Been working on a project from Dorico 3.5, converting it to the 4.0 versions up to the last 4.3 update.
The project file keeps getting slower and slower to edit even just one item on the score.
Today I started prepping a sample file to attach to this post, and the program crashed every time I edited/deleted something from it.
Hoping to get some insights/feedback/recommendations from others here on this issue.
Dreading the idea of having to start from scratch.

Dorico (889.7 KB)

Thanks for your time and consideration.

If the problem is reproducible, please attach the project here or email it to me (at d dot spreadbury at steinberg dot de) with details of how to reproduce the crash, and I’ll look into it right away.

Thanks for the crash logs – I can see what the problem is. Sorry for the inconvenience caused. We will need to fix this in a maintenance release. We are planning one to be released quite soon, so please hold your horses, or return to Dorico 4.2 for the time being.

OK. I will wait.
Thank you.