Connection through the OPC DA interface failed, maximum simultaneous connection limit reached.

Hello,
It appears that your client is making multiple connections and adding too many OPC groups. Kepware cannot automatically disconnect the inactive client. It is DCOM responsibility to kill orphan threads. You can try restarting Kepware to see if it terminates those unused threads. However, if the issue persists, I recommend reaching out to the client vendor to understand why this is happening. You can also capture OPC diagnostics in Kepware to monitor the number of clients and OPC groups increasing. Please refer to the article below for more details.
https://www.ptc.com/en/support/article/CS280490