Spent three weeks last month trying to figure out why my drum machine kept drifting after 32 bars. Thought the synth firmware was broken. Turned out my cheap unpowered USB hub was polling at 125Hz and dropping clock packets every time I moved my mouse. Hooked it up to a dedicated PCIe USB card and the jitter dropped from 4.2ms to under 0.3ms on my scope. Stop chaining five synths through a dollar store hub.