What were you updating LrC from? What was the previous version?
LrC v10.3 is not a major upgrade, just an update. If you were upgrading from LrC 9.4 , to v10.0, then yes, updating from v10.2 to v10.3 No. Upgrading from say v9.4 to v10.3 yes.
Mind you, if you use multiple catalogs, you could be opening an old one pre v10.
Also, if you only use one catalog, but you still have previous versions of that catalog, LrC could be opening the wrong one, it may get most recent wrong.
Double check that LrC is trying to open the correct catalog. Use Windows File Explorer for that.
Have you considered refreshing (a.k.a resetting) the preference file? The preference file can get corrupted leading to buggy behavior (like opening the wrong recent catalog). The preference file will survive updates, upgrades, uninstalls, reinstalls. Note that some preference settings might revert to defaults.