I see in the forums that other people have experienced this problem. BUT having started to create a site for the first time since the CC2017 Muse update I cant believe its this buggy and the problem is known about.
In a 10 hour day today I have been able to get maybe 60 or 90 minutes work done, and I have had two sessions with online support both of whom put me through a totally pointless uninstall/reinstall process.
It's clear that you at Adobe know about this issue, I am tied in to Creative Cloud because I use several other programmes in the suite - all of which run sweetly so its not a memory of processing issue*.
Come on Adobe stop making nice noises on the bulletin board and do something!
*That includes Premier pro which I see from the performance log ion my PC needs far more resources.
I apologize for your frustration. The latest version of Muse that was released today has a number of performance fixes that can help. Can you update to the latest version, and let us know if you are still facing these issues?