Looks like dried lees/sediment. If that's in the bottom of an empty wine bottle, I'd say the wine could have used a few more racking cycles which can be accomplished by bulk aging and racking every other month. If that's in the bottom of an empty carboy after racking then it's typical but, again, I'd say it needs a little more time and another racking cycle. I just racked 2 batches of wine for the second time during the bulk aging cycle and there was nothing gunked up on the bottom of the carboy like that but there was during the first racking. It will go away gradually as sediment is removed from the wine after each racking.
Its been awhile since I've been on been busy moving houses, work, and kids. I have 20 gallons of muscadine wine and this is the only carboy with this stuff at the top. after the first months racking I haven't racked any of it even once. I plan on doing it soon as in this week. I made the stuff mid July I believe. I guess add kmeta whats the recommendation?
I added a bunch of sugar and had a higher gravity yeast my thought process was have a high enough alc. level and not have to worry as much. I had tried some early october and it tasted fine to me even young.
Definitely not tartrates, they look more like salt or sugar crystals. Looks like a yeast bloom to me. Spray a little 10% meta solution on it and see if it goes away. If you haven’t added meta, I would, unless you are going for mlf.