I had a Zacama on the battlefield and a Trostani + 2 tokens generated by it. I pushed another one onto the battlefield with Vivien’s Invocation. I would have expected putting another Trostani onto the battlefield to trigger its ETB effects. I am convinced the extra tokens were not generated. I don’t remember for sure if the pump effect still happened, but if I recall correctly it did (granting a +1/+1 to my token stack and to Zacama herself).
While this may be another “summon vs cast” situation (which is still super ridiculous and confusing to begin with), but the description of Trostani does suggest this is supposed to be an ETB effect, not a cast effect.
Thank you for reporting this. I can confirm that the team is currently aware of this issue with Trostani Discordant’s Tokens. I’ll add this to the bug list for reference.