This happened to me yesterday and I found the problem
May be the tangle detection system, when the AMS cant feed filament at regular speed/force (maybe because you placed it wrong or the PFTE tubes are tigh). The printer thinks the spool may be tangled and purges a bit of filament to check if it can feed a consistent amount of it.
See the part where 4 PFTE tubes meet in the extruder, see how it moves up and down, if it moves down fully it alerts the printer about a tangle
See related info searching in the wiki for: Introduction to filament tangle monitoring
Solution: Place your AMS in another position and check if PFTE tubes are wide angled so the AMS can feed filament constantly without aplying too much force