Hi, so I am not sure what you were doing prior to starting this plan but it is very common for someone to keep training moderately hard most of the year and their FTP never improves or very little. If you were stuck at a specific FTP for a long time this could be your case. I also know this can be scary to see an FTP drop starting a new plan. Our plans are not like TrainerRoad’s or all the sweet spot plans out or even harder plans out there that are trying to give everyone immediate gratification of improvement. We are focused on the big picture long term and making you a heathly, competitive cyclist. Quick short term gains are not a part of being the best you can be unless you are right before your primary race or performance season (peak).
The most typical way to succeed in achieving continual improvements is through periodization which includes periods of up and downs in your FTP but each season can be a little higher than the last assuming you are riding at the same or slighly longer durations and following a reasonable plan for yourself.
Coach Jack plans start easy, so if you were doing a base period before this you might see a small improvement in FTP in the first 6 weeks but if you were doing something harder than it would be completely normal it would drop a little since CJ plans start easy. Personally I would say a 3w drop starting your build period is great 
because that means by the end of your build and especially the end of your peak you should see some solid gains.
I don’t know if this is reassuring enough but if we need to look deeper into what you were doing prior to starting this as well as the exact plan that would be great. Starting with for example the weekly strava hours chart for the last year is a good place to start.