This sound familiar was same here but in an other sequence and other controller NVEM v2 4 axis instead of NVUM.
I had your second problem first after 1 day of playing, I noticed the communication led (green Ethernet) on the NVEM blinked much
slower as when working. Contacted the seller with a movie attached and received a new one but had to wait 5 weeks
as nomore available from the EU warehouse.
The second NVEM works like a "charm".
Meanwile I purchased a spindle
Aircooled 2,2 Kw 3phase 300Hz 18000rpm collet ER25 (didn't find ER25 400hz 24000rpm as aircoolled and ER25 was main goal, was not easy/cheap to find in this setup)
Huanyang 2,2 Kw inverter mono phase 220V
The spindle is controlable from Mach 3 with M3 and M5 commands without external relay as mentioned befor,
just have to check if rpm is displayed correctly with external hand rpm unit
Grammatical errors are for free as google translate was helpfull