Sewing Machine Not Stitching?

I own a Carina Professional computer sewing machine and today I am in absolute despair. I've been trying for hours to troubleshoot the problem.

The machine has already been to a repair shop last year (for which I payed 80 Euros). It worked perfectly afterwards, but since then I haven't used it.

The machine made one short stitch line and suddenly stopped sewing. The bobbin thread doesn't go up through the fabric. I re-threaded both threads multiple times, changed the needle, being careful with the bobbin direction and needle position, and checked underneath the plate to see if there's any lint.

I removed the top-down bobbin case and observed the hook. The bobbin thread is picked up only after threading and once up it just stays there. The hook picks up the upper thread, but once released, the upper thread doesn't take the bobbin thread with it. During the troubleshooting I managed to make the threads lock once or twice, but not reliably.

I thought maybe it is a slight timing issue, so I made a couple of bad phone photos of the hook and needle's height. Yet I do wonder how a machine that hasn't been used for a year and is straight out of the repair shop can have a timing issue.

There is no service/repair manual I could find for this machine and I am not quite sure how high the needle's eye has to be when the hook's point reaches it.

Anyway, I don't have the means to invest in another expensive shop repair and this problem I find very weird. Does somebody know more about this?