What i cannot explain is this:
https://www.screencast.com/t/KjdmbwZd8Anx
That was one of 4 back to back tests i just ran – and it passes LCP, whereas the other three waivered between 3.2 and 3.6s.
Reading some git issues on ChromeDev and Lighthouse and other users have reported similar problems where LCP is not being calculated correctly – seems to me the simulated mobile test they provide has got a few bugs in it….
It may be worth giving it some time to see if Field data collected by Google reflects real world timings and not this simulated ‘nonsense’
Last thing you could do is test a post without a featured image background for the hero.