"To break it down, if system 1 has the company file open, the second system cannot access at all until the first system closes."

- Did you ever fix this problem? We also have this problem on one of our Quickbooks terminal servers but not all the time, just randomly it will occur. A few weeks will go by where terminal service users and network users are working fine with Quickbooks then bam! ... no one on the network can open the file until we reboot the server. 

Very frustrating, we've been dealing with this since about Quickbooks 2019 or 2018. Never happened before an upgrade. 

I feel like the best experience we had was possibly 2016 or 2017 with this configuration but along the way Intuit introduced this very annoying bug.