I don't know if this will help as I've not had this on ICTO but I've had a similar stock issue where batch detailing got changed after the event which caused a weird -/+ listing in locations.
Ignore if you don't do lot batch but if you do, it might be something?
Example: SKU01 shows as overall as 0, but on batch detail had AB -100, CD +100.
A User had done a change on the original Assembly build and changed the batch detail (From AB to CD) after an IF had been posted. This meant the IF had shipped a batch that no longer existed resulting in the AB -100. Whilst the AB had put CD +100 on stock.
Might be some weird stock detail mismatch on IF/IR etc?