It seems that updating from ViX 5.2 039 to 040 jams the box after reboot. At least if tuners are similar to my box:
2 x BCM3466 and 1 x TT3L10 set as T2.
Obviously problem is caused by faulty VU+ 4K drivers 2019.04.24. Same happens with OpenATV 6.3 and PurE2 images. Only VTi image does function with these drivers in Ultimo 4K box with mentioned tuner combination.