3.8 year old suddenly sleep gone to pot. Major meltdowns. Help!

[hufflepuffle]

Sorry it's long. Trying to get all in so as not to drip feed.
Our 3.8 yo DS has been sleeping in a great pattern for well over a year. Suddenly within last 2 months or so it's got very bad. Total refusal to go to sleep. Screams house down. In a toddler bed with short rail. Never got out. Suddenly climbing out.

Things we have tried. (Obviously not all at once)
Moved bedtime later, to about 8 from 7.15.
Got bedside lamp with dim setting incase was afraid of dark. (All this did was got him climbing out of bed. Joy)
Sticker chart, 2 stickers, 1 for going to sleep, 1 for staying in bed. Worked at start then novelty wore off.

Result every single night now is calm bedtime followed by HIDEOUS screaming the moment door closes. We have done variations of ignoring this or responding. Sometimes calms sometimes not. Either way we eventually give in and let him come out of room.
Last 2 nights has ended up with him coming down and having blanket on sofa. Night before was a 2 hour battle. So we've given in. Asleep within 5 bloody minutes. DH carries up asleep.

THEN woken screaming house down at 3 am. First night ended up down stairs watching bloody Clangers to calm him. Last night in to our bed. Who knows what tonight will bring. Before the coming in to our room he was waking screaming at 6.

Oh and there's a 16 month old DS asleep in other room. So there is a limit of how much screeching we can put up with. And I know for a fact most of the street can hear the screeching.

Generally having an emotional time right now. Lots of mega overreactive tantrums happening. But to be fair they are improving. Funnily it seems as they get better, nights get worse. Like he has to get it out somewhere.......

I do think it's an emotional phase and he's processing a lot but I'm very afraid we are getting in to a new habit that he will get quickly attached to.

I don't think it's nightmares as he doesn't tell us about anything. Nor terrors as he is fully aware. It's just a screeching 'I want to go downstairs /in your bed'.

It all sounds ridiculous. In a 'just bloody stand firm' way. But we can't. I actually think he would scream all night.

I thought we left all this shit behind a long time ago.

[hufflepuffle]

Oh and it was def all precipitated with him starting to play in street with kids nearby. (Don't panic, we our with him when he does and it's a cul de sac) Life started to get v exciting about that stage, I think.