we can consider all problem you mentioned, but I think it should be something common for all cells in NOKIA region. Because there are few cells with SD drop below 1 %. Thats why I suspect from counter/formula or something more common..
ps. we use sdr_4 formula
there may be another formula to discard Phantom RACH and bad impact on Abis fail counter..
For example, whats avg SD Drop in other Nokia network? if its around 1-1.5 % like we have, it’d be common NSN problem