I found these when upgraded. Well, those has been a while now, but this time I took a log.
[db:default] 'Messages section for sidebar' - checking...
Invalid version list in /tmp/discourse_theme_c64ff70a4cc7d614d9e88b106805c78f
[db:default] 'Unhide composer fullscreen toggle for tablets' - checking...
Invalid version list in /tmp/discourse_theme_4f18f6036fb93a7e2c8eca368c66ad09
[db:default] 'Discourse Highlight to Search' - checking...
Invalid version list in /tmp/discourse_theme_f7e393183be5f0189adb336c4602f071
[db:default] 'Discourse Wikipedia Lookup' - checking...
Invalid version list in /tmp/discourse_theme_8cf76b5d4fe5eac70cd636ee2487be35
[db:default] 'Accent' - checking...
Invalid version list in /tmp/discourse_theme_9796e5491667b1c43c7b9c680fc68ff3
Should I be worried?