On the desktop version, every time I try to open a request in my collection I get the “Request not found” error. I have to close Postman and reopen it and then the request I tried to load opens.
Welcome to the Postman Community! 
That doesn’t sound right - Have you tried using the Clear Cache and Reload option in the top level client window?
This is an example from the Mac client:
Hi Danny,
Thank you for your response.
I just tried Clear Cache and Reload and I’m still having the same issue.
Hey 
Could you also try fully logging out of your account and back in again?
Are you able to see the request on the web platform? (https://go.postman.co)
If this doesn’t solve it, we might need ask you to send your logs over to [email protected] so that we can take a closer look at your account 
I logged out and back in again but still having the same issue.
I’m not having the issue on the web platform.