I've encountered this on and off, across at least four different computers, sometimes in Firefox, sometimes in Chrome, sometimes both. I agree that this seems to have begun with an update early in 2019.
Uninstalling and reinstalling LastPass doesn't usually fix it. Nothing has been consistent about it, except that it's infuriating because of the massive time waste it causes.
LastPass support has been, sadly as usual, less than helpful about it.