DG switchover: 1. instance of (former) primary not stopping completely

2 Exadata with 2 node RAC, Grid control version 19.6 (primary, exa3) and 19.10 (standby, exa4), database version 19.9.0.0.201020 (primary, exa3) and 19.10.0.0.210119 (standby, exa4). So we have already patched one machine and will patch the other one next week, but are having big problems transferring dbs to the other machine.

DB is primary on exa3. Exa4 hold standby and is being patched.

After patching I do a switchover from exa3 to exa4. Standby DB is being opened on exa4 and becomes primary immediately. dgmgrl tries to stop primary on exa3, but does not succeed. This is what my db looks like in srvctl: 'is being stopped'