Hi Kate,
Yes, but I'm unsure if it's going to resolve your issue. Basically what we (me + ESRI Support) found was that once my Pro projects had too many maps/layouts in there (100+), it began to severely lag and my maps would never open. It took literally two months of testing and discussions. Lots of troubleshooting. They would literally just spin and spin for hours and do nothing. I have done a TON of trial and error, like closing the map frame, or closing the layout frame, and it would still spin continuously and never open up.
One thing that I am in the habit of doing now, which has greatly helped is that I always close any map or layout, to clear everything out, and then I save the Project. So that way, when it opens up again, there's nothing to load up and it won't get stuck. Essentially, they determined that there must have been some sort of glitch, or bug in a previous map, and once that existed in the project, there was no going back.
I highly recommend Delpha from ESRI - 888-377-4575 is ESRI's phone number, not sure if this is a direct line to her or not. But she was incredibly patient with me and does not give up.
According to my notes from ESRI, they ran Procmon on the machine while opening Pro to see if it caught any glitches in local data, as well as Fiddler to check the same things. We also created a new local directory, created a python script which automatically exports the maps and layouts (basically saves a copy, except directly from Pro, rather than file explorer). This way we could troubleshoot and see if those copies would open up. We also of course tried copying maps/layouts to a brand new project. Ended up sharing the project package with her. It was eventually determined that a particular map/layout was the cause of the issues moving forward with the Pro project - maybe corrupt data, etc.
I honestly do not recall what EXACTLY fixed my issue. But I do know now that I am working with multiple Pro projects, rather than just one. So as an example, I have created one for: Planning Board Maps, Properties, Asset Management, Data Edits, Synced maps from AGOL/Enterprise, etc. So that everything isn't all in one project. And like I said, closing out the maps/projects then saving the project has helped me greatly.
Thank you for sticking around with this lengthy response, but I think it may help you.