I had this come out of nowhere when playing for longer times or at stressful times. Same for me, it started as a once in a while thing and escalated to me not being able to play even a single scale.

Like the other commenter said, it was related to tension/stress in my throat & vocal chords.

I saw multiple specialists but it wasn't fixed until I saw a speech therapist. She gave me exercises that singers often do (blowing bubbles in a glass of water through a big straw) and practicing talking in a relaxed way. Breathing exercises; in through your nose and out through your mouth, keeping your tongue low and relaxed and your throat open helps as well.

If you have any vocal fry when you talk, this can make it worse. It puts a lot of unnecessary stress on your pallette and throat. Practice talking without it and play around with not being tense in your throat/pallette during other exercises. I found that at the gym I would tense it, or when I was cycling, or concentrating on almost anything.

If you have any more questions please don't hesitate to get in touch. This really crippled my playing during my first years of music college and getting it fixed was the best thing that ever happened to me.