I've had this happen a couple of times.
Setup is Brandmeister, DMR FW V15 from this morning. I have one static TG and no dynamic TGs linked. There is a QSO going on on the static TG, and I can hear it through the OS2. I click the [X] on the OS2's BM Manager tab to kill the static TG, and I get the green popup saying that the TG has been unlinked. Plus, I verify that the OS2 no longer lists that (or any) static (or other) TGs.
The call in progress does not go away, so I click Drop Current Call. The call still does not go away, even though there are no TGs static or dynamic according to the BM tab on the OS2. [See graphic.]
Further, on the BM My Hotspots page for my OS2, 310 is still listed as a static TG. [See graphic.] The two attached graphics were snipped at the same time, one showing that the OS2 thinks no linked TGs but continuing to stream 310 audio, and BM saying 310 is linked static.