...and remember a windows server (OS) is not recommended or supported!
That is only true if a user is running MC on the server itself. If a Windows Server is being used as a media file server/NAS, and MC is running on another (player) PC, then there is no issue.
It sounds like Forbigd is running the Windows server that way. Correct Forbigd?
If my interpretation is wrong, please provide a more complete description of your network, server, and MC setup Forbigd.
Nobody has really come up with a full explanation for these hangs, or "pauses in response". There have been a few threads discussing the issue though, and I have found some good information in those threads. Worth the research, although it sounds like you have already done some of that.
MC is waiting for something, but what that something is can be very difficult to determine. MC is very multi-threaded, but it still has a primary thread that does a lot of stuff, and that seems to be the issue here. The only way to really work out what is going on in a specific installation and environment, such as this one, is to use some of the available tools like Process Monitor and other tools from
Microsoft Sysinternals or elsewhere. But using those can be a difficult task with a big learning curve. The MC logs may provide some information, but it may not be specific enough, particularly when MC is waiting for an operating system process, such as file access.
It is pretty likely that the issue is related to the speed of access to the media files on the Windows Server, or the configuration of the server, such as memory assigned to caching, look ahead in reading disks, and so on. Waking a whole RAID array is an obvious issue, if it is allowed to sleep. But if this happens very frequently, and the RAID array isn't allowed to sleep so frequently, then I think the best thing you can do is optimise your Windows Server. That used to be a very technical task, to get the best efficiency out of a server. I don't know how hard it is these days though.
Oh, if your RAID array is nearly full, that is sure to slow it down. But you said this has been happening for years, and I assume that the array hasn't been nearly full for years?
To test that this is a network and media file access issue, just copy a few media files to your PC locally, then create a new MC library and import those local files only. Then use that new library as you would the original library and see if the problem occurs, and if it is as common.
Another test is that you could exclude all media files in your Antivirus software, rather than just the MC programs. As you have so much media (75TB!) it could just be that your Antivirus is constantly trying to scan, or finish scanning, all that media. You could run this test temporarily, and if this is the problem, perhaps a full scan of the media file from the Player PC might stop the ongoing scans causing an issue. I honestly don't really think this would be the problem though. If you also run Antivirus software on the Windows server you may also have to do a full scan there, as it would be a separate database of scanned files. Double whammy.
Another possible issue is that MC uses File System Events to detect if there are new files to import via Auto Import, if those events are reported to the operating system. When everything is run on one PC, File System Events are visible to MC. If media files are on an external device, such as a NAS or maybe a Windows Server, then File System Events may not be visible to MC. In that case, MC needs to scan the drives associated with Auto Import to look for changes. That can take time. A lot of time if the media is on a 75TB RAID system. I think that Windows Servers can report File System Event to other Windows systems, but I'm no expert in this area, so don't know for sure. If you find that the issue is indeed a network response issue, you may wish to look into this.
I don't think a rebuild of MC would help, especially not re-importing everything. That would achieve nothing but lots of work and anguish. I don't think rebuilding the Windows PC would help either, as long as it is up to date.