I can confirm packet sniffer on 4.17 and 5.7 does not capture properly the frames that come out of the MT router. VLAN info is missing where as they should be tagged.
Frames coming from outside clearly show that they are tagged.
I can also confirm that DHCP does not work properly with v5.7 on a VLAN interface.
I think MikroTik should invest in QA, testing, debugging or sell the business to some company that can release updates without so much bugs and incompatibilities.