We had an internal ATA go dead after a few weeks. The Vendor replaced the internal four port card with a external ATA until we could get the RMA back. The Ring Pattern was set at Internal (3) and External (1). The fax machine is a Brother 850. After we switched out the internal for the external then the faxes were not being received. The machine would ring but not receive. I changed the ring pattern back to I(1) and E(1) and everythings was working fine.
I tested this after we got the RMA back and it worked fine for any Ring Pattern.

I am the only lucky guy stumbling on these cazy things.

No- you're not the only one.

The issue is old.

The fax machines and other 2500 devices may not recognize ring patterns 2 or 3 on the NBX.  The ATA card does not generate 'true' AC ring current to the device.  The devices such as your fax need a constant burst of simulated ring current from the NBX- thus the setting of 1 however-- you posted that you also have a setting of 1 now, also for your external/internal calls.

NOT a GOOD idea.  The two settings MUST be different.

HEADS UP.

My problems is that it works one way but doesn't the other way. Setting it back to 1 works. Then the cazy thing is we are talking about internal call setting that make a external call not work.

The ATA acts as an "internal" device...so yes, when you change the internal setting in Sys Config it can make the FAX fail to recognize the simulated ring cycle.

Itz all about "cycles" or lack of.