It worked (usually!) on my AZBox Ultra, but did struggle to get it when first going to the channel (and sometime freezes for a bit). Anyhow, on another site someone said that the PCR for the channel is missing from the PMT Table. Therefore, I just did a manual channel entry in PID Edit in Advance Scan (don't know whether that is the same place you do manual entries in the AZBox ME or not) and it works fine now.
The PIDS for the channel (scanned in) are PMT PID: 240, SID: 15, PCR: 8191, Video PID: 241, Video Type: H.264, Audio PID: 244, Audio Type: MPEG-2.
The manual entry I did changed the following: PMT PID: 740 (added 500 to avoid any other PMT PID in the table), SID: 115 (added 100 to the SID, again to avoid any other one), PCR: 241 (same as the VPID, which all other channels in the mux also use). Rest of the PIDs are the same. That corrected the problem completely.
When FNX first appeared in "test mode" before disappearing for a bit, I did not have any problem with the channel, so it has only been since they re-added it to the mux that the problem appeared.