Brewed with harvested yeast but fermentation may have stalled

tl;dr: Harvested commercial yeast and everything looked fine. Fermentation seems to have stopped without reaching FG. Some banana flavours. Is it ruined?

So I tried harvesting some yeast from a Young's Special London Ale (as an Englishman in Australia I thought it would be nice to culture a yeast from home). Followed the usual steps using a fairly weak wort and built that up over about a week.

Brewed an extract kit (as I'm out of grain) which gave me an OG of about 1038 and pitched at 22c into temp controlled brew fridge. Fermentation started slowly the next day then sped up as usual.

Bubbling slowed right down after maybe four days, which is not unusual for my liquid yeast brews and seems to have stopped. I've taken three hydrometer readings over the past three days and they are all around 1022. There is a sweet flavour to the sample so I'm guessing it hasn't finished and maybe a hint of a slightly off or banana flavour.

So has it stalled, and if so is there some sort of rogue yeast action going on?

My plan is either to pitch the dried yeast that came with the kit and dry hop or ditch the brew.

Any thoughts?