2019 was a weak spot - desperately unpopular leader, two established MPs going and non-locals being parachuted in. Fletcher held onto her seat comfortably so, with the new MPs having had time to show what they can do (and they both seem to work quite hard) you'd think they'll establish themselves more.
2019 was a case of as you say a deeply unpopular leader, brexit (remember cov voted solidly leave, while the party had an awful remain position) and a badly fought ground game.
We will see Starmer be a lot more popular when we can doorstep again, sultana admits she wasn't great on the campaign (Cunningham used to seemingly knock on most doors himself) and a load of other things like being seen to actually like the country you want to lead.
Hartlepool will be interesting, if Tice doesn't run in some form (Brexit/reform/whatever party) be interesting to see if the medias weird idea that all BP votes will vote tory if the BP aren't running idea is correct.