Password managers generally use CSV, avoiding vendor lock-in. However, back when Lastpass doubled their subscription cost (yes, doubled, literally) I switched to Bitwarden. At that point, there was some issue with exporting passwords with a certain character (IIRC it was ; or #). I ended up changing the few passwords which quit working.

As for OP, my take is you clicked a bad link triggering a zero day vulnerability in your browser, or perhaps you logged in on Lastpass via a VPN or Tor? Its pure speculation though.