It sounds like these task windows may be opening minimized or off-screen, which would allow them to appear in a small preview window when you hover over them on the Windows Taskbar, but would prevent them from being viewed normally and cause Sage 50 to behave as though its still loading.

We have steps for fixing the issue in the knowledgebase article at this link: https://support.na.sage.com/selfservice/viewdocument.do?noCount=true&externalId=11449

Normally using the steps in Section 1 of that article to reposition the window should suffice.  However, if that doesn't work I would recommend going through the remaining sections in order, as they're arranged from most to least common solutions.

Is the database server on your server computer running at high CPU after a few people sign in?  We're having some serious issues related to 2023.  We're having to revert to 2022.

I found the problem.  I added "quantity on hand" to inventory list & it slowed things down to a crawl.  We're using Windows Server 2012R2.  I know it's on the way out & we'll be upgrading our server & operating system sometime next year.  

I suspect the slow issue you're having is also related to the database issue with 2023.  If you revert to 2022, I suspect you will not have the same slowness issues.  Furthermore, you do not have to revert the database as the database wasn't converted between 2022 and 2023.  You don't have to worry about data loss as the file can be reopened in 2022 after being opened in 2023.