I would run dental floss through the thread path before making adjustments. I find a bit of old thread making its way through the path, messes up the tension.
Make sure it is UNWAXED dental floss or you will make a big mess!
Hopefully by now you have sorted yourself and the problem out and are up and running again
Makes me think of my Dad years ago teaching me about screws. He always said. Righty tighty, lefty lucy! lol
We hear that here too.
And my teacher always said upper tension is lower tension, so reset your bobbin - this was for Janome machines and may not apply to all brands, but it has worked for me.
And my old teacher said NEVER adjust the bobbin case screw!
I was taught the same lol
With the Janomes I had there was a mark at which the bobbin screw was set. To reset it you loosened the screw and then put it back to where it was originally.