If the PBX does not send the recipient number in a block for incoming faxes, the fax reception service may already evaluate the recipient number if it is not yet complete and therefore cannot find the user in the XPhone server.
To avoid an early evaluation of the recipient number, you can activate a waiting time:
In XPhone Server, under SYSTEM SETTINGS -> FAX -> GENERAL, add a new parameter called Fax2Mail\CapiForceInfoEvents to the ADVANCED SETTINGS, set this value to 1
The default waiting time is 2 seconds. If you want to change this, set another parameter named Fax2Mail\CapiInfoEventsTimeout and set it to 3000 if you want to set three seconds instead of two seconds.