Multiecuscan

In some cases MES skips some modules in "Scan DTC" procedure.
For example, when I use ELM327 Wi-Fi without any adapter cables
and start "Scan DTC", progress bar goes to 25% very quickly and skips
test of "Engine module" for errors.
What is possible reason for this issue?

Depending what car you have, there will be a number of interfaces on the OBD connector.

Unless you are using MES Multiplex, MES can only connect to one interface at a time and Scan DTC must be run once for each of the interfaces using the adaptor cable appropriate to the interface.

@bowdenandymecom read one more time what he wrote - he ment that some modules are sometimes skipped during scan. seen that happen with Giulia/Stelvio PDC module on v4.8

I suppose reason for that behaviour (sometimes read expected modules and sometimes doesn't, with or without adapter cables) is the lost of connection between interface and laptop. This issue was happened only once or twice and next time all was OK.