Standard 9x7 insulated garage door, standard torsion spring. New tracks, guides, rollers a few months ago. Garage door opener is standard chain drive, probably vintage when the house was built (2008 I think).

A week or so ago, I opened the garage door to leave, but it only went up about 1/3rd of the way. Didn't seem to bind on anything, just quit trying. Closed it (which worked), and tried re-opening but got to the same height and quit again. I pulled the release rope and pushed the door up. Cycled the opener, and when it caught it closed the door with no problem, then opened it with no problem for a couple days.

It's gone through this about 3 separate times now, no real pattern to time of day, weather, how long it's been sitting, etc. Opens partway, release and manually open, cycle the garage door opener, then it opens just fine for a couple days. No squeaks, no bent track or rollers (evidenced by ability to open manually easily).

Is it the garage door opener?

Did you check to see if one of the springs is broken?

Not specifically, no. It's a single torsion spring, which I installed a couple months ago when I replaced the track. I assumed it was functioning since I can open it manually (insulated door is stupid heavy). I will check it for cracks, slack, etc this evening just in case though