I found that tdm()/tom() are based off BarZone time while day()/month() functions are off UTC.

This creates a situation where for BarZone=ET, the time period from 00 to 400/500 UTC technically belongs to the ' last trading day' according to tdm() but is already the 'first day' according to day().
Not expected and illogical.

Can this inconsistency please be resolved in some way?

Why don't all time/date functions respect BarZone (i.e. return time in BarZone time by default)?

It might make sense to make tdm() respect EndMarket (which is in BarZone time)...With EndMarket=1700ET, 1800 ET will belong to the next trading day - which it is..