OK, so I did.it probably is enough to stop corosync and pve-cluster on node 13, check the status on the other nodes, and if that looks good, start the services again on node 13.
there is one peculiarity in the logs that i am not sure about, I'll have to take a closer look - when node13 joined corosync logs that its ready after pmxcfs logged that it started synchronization, maybe that caused some inconsistent state or caused something to be lost, but it might also not matter at all or just be a log ordering issue with no consequences.
Afterwards, I could login in web GUI 101, bot not on 102, 103, 104, 105, 106 (all hang), but 107 I can. On 108, 109, 110, 111, 112 I cannot login (all hang), but on 113. On the three were I can login, I see 101, 107 and 113 in green icon, all other in red. SSH works on each even with key now.
The pvecm status is accordingly; on 101, 107 and 113, only 3 members are listed, but on the others, all (101-113) are listed. Apparently the command is fast on the others, but often takes multiple seconds on the 3. I added details in attached script-4.txt.
Thank you so much that you help!