When I tried doing that RNG ages ago, it always failed for me too. Never got the imposter ditto grotto RNG to work.Not sure how you figured out you hit the correct Timer0, but yes could do with advances or due to the fact that maybe you don't have all of the grottos filled before the one you're interested in. Possible also the tool is bugged? But I really haven't been keeping up with Pokefinder releases (and is probably more likely the formers)
I'd recommend starting with something easy, like a wild mon with no NPCs or a stationary so you can use the adjacent tool to see what you're actually hitting. More often than not it's Timer0 trolling.