Hiya, I've possibly quite an obscure situation here - just upgraded from Ubuntu 14.04 to 20.10, which equates to a picard upgrade from 1.2 to 2.4.2. (Also tried the musicbrainz-developers/daily ppa today and verified the problem is still there.)

This isn't a particularly high priority as I can work around it by deleting my existing settings (rm -rf ~/.config/MusicBrainz) and it starts from scratch okay, but I thought you might like to know anyway.

With my previous config file in place (attached) startup gives this python traceback and aborts (repeatedly.)

I: 13:42:59,450 /usr/lib/picard/picard/config._backup_settings:274: Backing up config file to /home/dave/.config/MusicBrainz/Picard-1.3.0.dev1.ini
E: 13:42:59,459 /usr/lib/picard/picard/config.value:125: Cannot read setting/preserved_tags value: unable to convert a QVariant of type 10 to a QMetaType of type 9
Traceback (most recent call last):
File "/usr/lib/picard/picard/config.py", line 121, in value
value = self.raw_value(name, qtype=option_type.qtype)
File "/usr/lib/picard/picard/config.py", line 104, in raw_value
value = self.__qt_config.value(key, type=qtype)
TypeError: unable to convert a QVariant of type 10 to a QMetaType of type 9
Traceback (most recent call last):
File "/usr/lib/picard/picard/config.py", line 247, in run_upgrade_hooks
hook['func'](self, *hook['args'])
File "/usr/lib/picard/picard/config_upgrade.py", line 121, in upgrade_to_v1_3_0_dev_2
_s[opt] = re.sub(r"\s+", ",", _s[opt].strip())
AttributeError: 'list' object has no attribute 'strip'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/bin/picard", line 3, in <module>
main('/usr/share/locale', False)
File "/usr/lib/picard/picard/tagger.py", line 974, in main
tagger = Tagger(picard_args, unparsed_args, localedir, autoupdate)
File "/usr/lib/picard/picard/tagger.py", line 244, in _init_
upgrade_config(config.config)
File "/usr/lib/picard/picard/config_upgrade.py", line 330, in upgrade_config
cfg.run_upgrade_hooks(log.debug)
File "/usr/lib/picard/picard/config.py", line 250, in run_upgrade_hooks
raise ConfigUpgradeError(
picard.config.ConfigUpgradeError: Error during config upgrade from version 1.3.0.dev1 to 1.3.0.dev2 using upgrade_to_v1_3_0_dev_2():
Traceback (most recent call last):
File "/usr/lib/picard/picard/config.py", line 247, in run_upgrade_hooks
hook['func'](self, *hook['args'])
File "/usr/lib/picard/picard/config_upgrade.py", line 121, in upgrade_to_v1_3_0_dev_2
_s[opt] = re.sub(r"\s+", ",", _s[opt].strip())
AttributeError: 'list' object has no attribute 'strip'