As of the upgrade to 10.5.9 (autoupdate) I was seeing a large number of warnings in my mariadb logs saying attribute lengths of 569/570 were truncated. When I looked at global variables performance_schema_session_connect_attrs_size was at 512. This is a variable I did not define specifically and the default is supposed to be -1. When I set this setting specifically and restarted mariadb on the nodes the errors went away.

2021-03-22 10:31:54 142120 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:31:58 335410 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:31:58 335420 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:31:58 240646 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:31:59 335410 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:03 408238 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:06 335407 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:07 335412 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:07 142120 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:08 335418 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:10 335407 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:10 429847 [Warning] Connection attributes of length 569 were truncated
2021-03-22 10:32:11 335412 [Warning] Connection attributes of length 569 were truncated