I have tested it on my end, the bug defenitely still exists.
You see, the trigger eff of returning back, is coded on the Painter who made the banish.
Iff the painter remains on the field, the trigger eff will resolve normally and the opponent monster will come back, this is fine.
However, if that same painter is banished by a canvas eff, on the same Standby Phase, before using the trigger eff, the opp monster won’t return, effectively making a permanent banish.
I suspect this will happen if for any “X” reason said painter is not on the field at the Standby Phase, shuffled to the Deck, sent to the GY, Eff to Special Summon negated, you name it.
The solution should be, that the opp monster returning should be a mandatory action to happen, coded on the player, not on the painter who made the banish.