Has there been any other work done on the purifier like the servicing to the systems supplying water to the purifier during the automatic process control? If so I would check the valves were assembled and functioning correctly, the coil connections are in good condition, verify that something hasn't been crossed with the hoses or the coils & wiring and that the volume of control water to the purifier is not somehow being restricted .
Has the purifier drive been inspected or serviced recently? As it also sounds like there could be an issue with the purifier drive which may be preventing the purifier bowel from coming up to full operating speed. Bowel speed could be affected if the pads for the centrifugal clutch or drive belt are worn out or not assembled properly (pads put backwards or drive belt not properly tensioned or auto tensioning not working) or if for some other reason the drive motor is not coming up to to full operating speed (Faulty VF Drive) If the bowel speed is too low for any if these reasons, the bottom parring/water control disc would not be able to supply sufficient pressure to close and keep the sliding bowel closed.
I would also check and change, if haven't already done so, any nozzles and seals associated with the bowel closing water space. I'm not familiar with this particular purifier however if there is a set of coil type springs in the underside bowel assembly similar to that fitted to Alpha Laval Purifiers. I would also suggest replacing all the springs in the set, as I've experienced bowel closing issues on Alpha Laval Purifiers similar to what you are experiencing caused by these springs becoming weakened over time.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"