Thank you for your question and reaching out.
- Please verify that Server is Activated using proper Windows License and Edition.
- Please check Event logs during the Time of disconnection of users or RDP for any clue.
- Disable any Antivirus program or Windows firewall you may have for temporary purpose.
- Disable IPv6 from Lan card properties and Verify Virtual switch configuration for this VM.
--If the reply is helpful, please Upvote and Accept as answer--