Did Glitter recommend the Amazon flux you used? Have you tried the flux that Glitter sells?
U.S. Solid Copper Welding Paste Flux 40g ? According to
@byke , it made all the difference spot welding copper to copper on his stash of 32135 cells. Before he got the flux (which arrived a month late), he burned out his Glitter 811H by keep increasing power (and still didn't achieve successful welds onto 32135 cells). Glitter sent him a new board which got his unit back in operation at which time the flux arrived, which was the magic potion that made the difference (for copper to copper).
Note: the above info is via pm between
@byke and myself. I do not own a Glitter 811H or any spot welding experience to speak of. I bought 48 32135 cells from him and built a battery for my scooter/ moped by soldering it together with copper strips. The pack turned out well (so far) and is undergoing test on the scooter.
edit:
This is my first battery build. Configuration below is temporary for testing. It has no BMS currently (I do have 2 JBD waiting to be installed). Wires will be shortened with proper termination.