Panasonic DMR BWT-720 weird behaviour

[Monty Python]

So recently it's decided to stop playing some discs. Take the Alien boxed set - Alien and Aliens play to the 20th Century Fox logo, then I just get a black screen and it refuses to budge. Alien Insurrection - plays perfectly. Prometheus also behaves like Alien/Aliens. All the discs play fine on my £30 Samsung player, so it's clearly the Panasonic that's the issue.

Can't see anything obvious - the last firmware update was back in 2016, and I've reset it to shipping condition without success.

Any ideas?