Soily smell in bathroom

[chumley0312]

A good while ago, a dodgy plumber decided to hack off the soil pipe under the bath to remove the boxed in section of the pipe and left it open. Anyhow subsequent bathroom renovation put an AAV on which failed a few years ago and a replacement fitted. Last weekend we started to get what can be described as soily smells in the bathroom particularly if door been shut for a while. It's not bad but noticeable. It comes and goes some days don't smell anything. It's like a soily foisty water smell worse if you sniff around the bath panel. (AAV under bath). I'm suspecting AAV has gone partially faulty again. Couple of questions

Is it likely the AAV again

Should I just replace AAV again and forget about it.
Should I be considering reinstating the soil stack back to how it was.

Thanks