Not sure I can help, but can share my FEC 120 experience.
FEC 120 took over an hour to get up to temp (235F) on my first cook. Cookshack said they had a couple 120's at the plant taking long periods to get up to temp. All my cooks since (over 20) have only taken 20-30 minutes to get up to 250F - 275F. My guess is that the auger took the entire first cook (butts for 14+ hours) to get completely filled with pellets.
Also during the first cook, I checked the firebox compartment several times (out of curiosity) during the 'get up to temp' period which led to periodic temp drops. I no longer open the firebox door during a cook, nor do I open the smoker door for the first 2+ hours of a cook. I use Cookshack hickory pellets.
I have been cooking large loads of butts, briskets, etc. but have yet to pack the FEC 120 full. I have noticed during cooking that there seems to be a 'burn/smolder' cycle for the pellets. The temp cycles within 10-14 degrees of the cook temp, dropping to the lower end during smolder while a more noticeable amount of smoke is venting from the unit (Example- cook temp is 250F but temp may cycle between 240F & 254F with smoke venting more at around the 240F level). This cycle also occurs while getting up to temp.
You'll hopefully have a chance to talk to someone at Cookshack soon. Good luck.