It seems that 5.2 002 will jam during boot in Ultimo 4K if you have Sundtek usb-tuners installed. Same thing is in ATV 6.2 and PurE2 images when VU+ drivers are 2018.10.05. When jam happens, just delete with ftp /usr/sundtek directory and boot again.
For some reason if I complain this matter to Sundtek, they insist me having chat with their system. Jus wonder why because I have explained this fault in Sundtek support.