Hi, I am new to the forum and the UP BOX + . But I had the same issue and I solved it. (the solution is highlighted at the bottom of the message if you don’t want to read the whole story)
For me I had a smaller printer and no issues at all with the same spool of 1kg Black PETG. When I changed to the UP BOX+ , at around 10 layers in the printing PETG stopped going out of the nozzle, I changed material temperature, layer thickness, speeds, nothing worked. I decided to clean the part where printer grabs the filament, it wasnt that dirty just a few remainings on the wheel at the same time i decided to change the Nozzle but i broke the new nozzle because i just put too much pressure in the turn, because i didnt know how tight it had to be, so dont do it as i did, anyways i just put the old nozzle back (you might see some melted material in the inside of the nozzle, dont try to clean it thats normal, and read the manual so you know how to do change the nozzle properly). So when I did all of that with the same spool in the old printer to discard the spool being an issue. It printed perfectly. While printing I realized that printer made a strange noise, I helped the spool to feed the printer and it stopped, so I thought it might be THAT !!! My Spool doesn’t really fit in the wheel of the UP BOX+ so I think printer needs to make too much effort to pull the filament and at some that creates issues and stop feeding the nozzle. I tried the same print and rotating my spool manually while printing, and no problem at all!
I didn’t try only the maintenance fix, but I’m pretty sure it was that the spool is too heavy and also the spool doesn’t fit correctly and produces too much friction inside the wheel so I will have to design an accessory for that spool to to make it rotate easily.
Hope this information is useful.