I've encountered this same issue after upgrading to Katello 4.1 (foreman 2.5.4). From the debug log, I think the issue is the ldap filter. It differs from the one when manually refreshing the groups. As a workaround I've disabled sync on login, and that seems to work.

# manual refresh

2022-01-11T14:18:28 [I|app|10ca67b6] Started PUT "/external_usergroups/my-ldap-group/refresh" for 10.8.160.119 at 2022-01-11 14:18:28 +0000
...
2022-01-11T14:18:28 [D|lda|10ca67b6]   op bind (41.5ms)  [ result=success ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   op search (13.2ms)  [ filter=, base= ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   op search (14.2ms)  [ filter=(cn=my-ldap-group), base=ou=Group,dc=example,dc=com ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   op search (50.4ms)  [ filter=(cn=my-ldap-group), base=ou=Group,dc=example,dc=com ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   op search (50.5ms)  [ filter=(|(|(|(objectClass=posixGroup)(objectClass=organizationalunit))(objectClass=groupOfUniqueNames))(objectClass=groupOfNames)), base=cn=my-ldap-group,ou=foreman,ou=G
roup,dc=example,dc=com ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   user_list (172.1ms)  [ group=my-ldap-group ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   op bind (11.8ms)  [ result=success ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   op search (14.1ms)  [ filter=, base= ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   op search (48.8ms)  [ filter=(cn=my-ldap-group), base=ou=Group,dc=example,dc=com ]
2022-01-11T14:18:28 [D|lda|10ca67b6]   valid_group? (75.7ms)  [ group=my-ldap-group ]
2022-01-11T14:18:28 [I|aud|10ca67b6] Usergroup (2) update event on user_ids 15, 15, 13

# user login

2022-01-11T14:15:22 [D|app|7bae0c9b] Updating user groups for user johnsmith
2022-01-11T14:15:22 [D|lda|7bae0c9b]   op bind (39.4ms)  [ result=success ]
2022-01-11T14:15:22 [D|lda|7bae0c9b]   op search (11.6ms)  [ filter=, base= ]
2022-01-11T14:15:22 [D|lda|7bae0c9b]   op search (13.1ms)  [ filter=(memberuid=johnsmith), base=ou=Group,dc=example,dc=com ]
2022-01-11T14:15:22 [D|lda|7bae0c9b]   group_list (64.5ms)  [ user=johnsmith ]
2022-01-11T14:15:22 [I|aud|7bae0c9b] User (13) update event on usergroup_ids 3, 2,
2022-01-11T14:15:22 [D|app|7bae0c9b] Post-login processing for johnsmith

Looks like at login the filter `(memberuid=johnsmith)` is used, which will only find `posixGroup`, and not `groupOfUniqueNames`, which what I use.