Highs compressor axial displacement

Dear all,
I need help, we have 2 BCL 406 centrifugal compressors which triped by high axial displacement at threshold of 0.5 micrometers despite the axial float is set to a minimum value of 0.25 micro. when we open the compressor we do not find a big change in float zone 0.26 micro. the two compressors are a subject of revamping of the vibration monitoring system. The old instrument for monitoring thrust
is a gauge bridge where the resistance of the gauges varies according to the axial thrust applied on the rotor. the new monitoring system presents two manitic probes from Bntely nevada installed at the suction side of compressor rotor. after starting the turbocomressor and when it reaches the complete sequence, the operator begins to increase the compressor speed (TNL), in order to move away from the surge zone, at this time the axial thrust increases up to exceeds the alarm threshold. when we start closing the recycling valve to load the machine, the axial thrust increases each time we close the recycling valve until the trip of the machine by high axial displacement. is there any explanation of this problem ?

Thank you