Hi Foedog..welcome to the forum . It sure sounds like the heli has the toilet bowel effect (TBE) . As you said , there is a recent thread here on that problem , I think the problem was something binding on the rotor head / flybar or a cracked part .
`Crab trim` ? What`s that ? Crabs move sideways..sounds like ? Have you/ can you switch off `crab trim` ? If so , is there any change ? I have a Solo Pro 260a..similar to the V911 and any hovering issues on mine are usually caused by worn links / ball joints ...oh , and crashes !
Maybe try re-binding the tx to the heli . Hope this helps .