I have the exact same error on my end.
-| 8/15 Migrating fs_used name...
-| + "Migrating fs_used name" failed
-| Traceback (most recent call last):
-| File "/omd/sites/home/lib/python3/cmk/update_config.py", line 146, in run
-| step_func()
-| File "/omd/sites/home/lib/python3/cmk/update_config.py", line 183, in _update_fs_used_name
-| cmk.update_rrd_fs_names.update()
-| File "/omd/sites/home/lib/python3/cmk/update_rrd_fs_names.py", line 186, in update
-| update_service_info(config_cache, get_hostnames(config_cache))
-| File "/omd/sites/home/lib/python3/cmk/update_rrd_fs_names.py", line 174, in update_service_info
-| update_files(hostname, service.description, service.item, 'cmc')
-| File "/omd/sites/home/lib/python3/cmk/update_rrd_fs_names.py", line 80, in update_files
-| filepath = get_info_file(hostname, servicedesc, source)
-| File "/omd/sites/home/lib/python3/cmk/update_rrd_fs_names.py", line 64, in get_info_file
-| host_dir = cmk.base.cee.rrd.rrd_cmc_host_dir(hostname)
-| AttributeError: module 'cmk.base.cee' has no attribute 'rrd'
It’s annoying, although everything works fine after the update. main.mk is already empty (only the first 2 commented lines).