Bladed Spokes and H Plus Son Formation Face Rims

As for chain tension, you're still not making sense, chains don't grow in length with wear, the rollers on the inside of the plates become worn and then don't properly fit the teeth of cogs/rings. It may have just slipped a couple of mm down in the dropouts.

Just buy a half-link chain and be done with it.

chains do get longer with wear. the old skool way of checking chain wear is to measure 12 links if the chain has grown 1/16 in it's possible to use it with new chainrings/cassette 1/8 and it's fucked.

*"For normal maintenance (chain-suck not an issue), chains should be replaced at about +0.5% overall "stretch". This +0.5% = 1/16" = 1.5mm over 12 link-pairs.
By +1.0% stretch (1/8" or 3.0mm over 12 link-pairs), chains will have done significant damage to both the chain-rings and rear sprockets. Then when you install a new (or low-stretch) chain, it will inevitably skip over the worn teeth on the rear sprockets during high-load pedalling ; this is very disconcerting and its impact loading will do further damage and will do it quickly."*