Gen 1 2nd gear issue ?

[Batfink]

On both my gen 1 I had the fun miss, or false neutrals. They normally meant I had to use the selector again. You said if felt like it missed but did it rev high?
Unless you chain is over spec on looseness or the rear sprocket teeth are extraordinarily worn I would count out skipping a tooth/teeth as the maths says it can't. Others with more than experience can help here.
I do know that, from experience with the gen 1, once plugs start fouling look further... Twice (do fife rent bikes) the best solution for me was to get injectors sonic cleaned. Solved theproblem instantly.

Probably didn't don't help but something is better than nothing lol