Bottom bracket harder to turn half way around

does this sound like a I need a new bottom bracket ?

When I turn my cranks with no chain attached, it’s pretty smoothe, no real noise and just goes for a while if I let it spin.

When I attach the chain I can turn about half a rotation freely and then it becomes stiff and seems to be in the same place each turn.

I think my bottom bracket is press fit type – it looks like cartridge bearing on either side – I’ve probably done a couple of thousand miles.

I did just change the cartridge bearings in my rear wheel & hub, think my chain is worn between 75% & 100% from the tool I used to measure.

this may be unrelated but im riding a lot on a turbo trainer – something is causing the chain to vibrate a lot in the lower / harder gears – but appears to be indexed fairly well.

Thanks.