Summary
The API call to list channel members no longer returns LastViewedAt
I can see this is deliberate, as git checkin ba86dfc5876b354b9d3c20ff45c08ca6f8426149 on 05 Nov 2025 adds code specifically to do this (unless you are logged in as the user in question, when it does set it).
Why has this change been made?
I have an important requirement to know when each user last logged in to Mattermost. I have been satisfying that by selecting the most recent date the user visited a channel (I have to check the channel members for all channels, anyway).
Is there an alternative way of finding out this information via the API? Note that I am not admin of the self-hosted Mattermost instance in question.