There are lots of great "trouble Shooting Hints" on the feed!!!
i REMEMBER WHEN I FIRST HAD a problem like this... I took apart the top of my machine. cleaned and oiled the spots, took the plate off and bobbin carriage and I was so shocked to see how the threads and lent collects there... a person I know who services machines said that each time you finish a project and before you start a new, clean out the feed dogs,,,using a clean narrow brush (like one uses for painting)about a half inch size) brush around the bobbin case, put in a new needle and fresh bobbin..
It works for me and never have a build up of lint..

I wouuld try a new needle. Turn everything off then back on, rethread both thread and bobbin, then cry if it doesn't work

This happened to me once and I looked for a long time to find out the problem, and it was a simple issue of engaging the bobbin winder by accident. Did I feel like an idiot!

I had the same problem and my machine was FILTHY!!!!

My dealer told me to clean often and oil. Seems Bernina's like oil. I have an attachment for my vacuum that I use to clean out my 820.

I have found that sometimes a lead thread gets caught somehow on the foot, the fabric just gathers up behind the foot and will not feed through

Well, I took Matilda to the Doctor today. Dr says there is definitely something wrong. She's going to give her a tune up and see if that will correct the issue, if not, she'll have to operate. :(

Clean out the lint. I can't make buttonholes on my Bernina when it is linty.

Update! I just talked to the Bernina Doctor, and poor Matilda just needed a tune-up. She's stitching along just fine now and she gets to come home tonight!

Yay! So glad you'll have a functioning machine tomorrow! Happy sewing.