As far as I know it is some offset in Hz from the supposed receive frequency (Downstream Freq.).
I think you still have a better offset, I have a remote with more than 10 kHz offset receiving small downstream (256 kbps) and still online.

Regards

Try telnet into the modem and issue the command 'spoof stats', this will tell you if you have a session count issue causing new sessions to appear to hang.

RX COF in Hz is the Carrier Offset Frequency...basically, the difference (in Hz) between the incoming frequency and the receiver’s reference frequency.      Have the hub check/confirm that your observed COF isnt exceeding your LNB stability configured in the RemoteRFT in iBuilder.  Stability configuration on remote (in iBuilder) specifies the bandwidth of the rx filter, and it should correspond to your LNBs specified stability. If you observe COF that exceeds the configured iBuilder LNB stability, you could have a couple of problems:

If the COF starts at at a high number such as >250kHz, and eventually fall back to within +/- 150kHz range, then the iDirect likely needs calibration (has a bad calibration file). Or, if the COF starts at some high number, and settles at a high number such as >200kHz, then you may have a bad LNB....the LO is off the specified frequency.

The above is working under the assumption that your acquisition range is +/- 150K.