Try contacting Janome and discuss it with them. You can raise the question about it being a known issue and the inability to access the area where the thread has been caught. I'm not sure in your case exactly where the problem has arisen.
Like most people I'm sure, I've had occasions when thread has caught, usually below the feed dogs and occasionally some miniscule piece of thread somewhere in the shuttle race/hook area and the machine malfunctions, frustrating as it can be, I've always managed to clear it eventually. OK I've sworn a few times, cursed myself for loading a bobbin which hadn't wound correctly.
Janome UK Ltd
Janome Centre,
Southside,
Stockport, Cheshire,
SK6 2SP, United Kingdom
Main
0161 666 6011
from outside the UK +44 161 666 6011