I use the app on my phone, and the website in the office.
I use a lot of comments for my cards (comments and activities section of the cards).
When I change a comment on my phone (app), for example add a line, and then later (several hours) open the Trello website (newly loaded) and then open the card. I can see the change I made, but when I click the comment to edit it, the changed lines disappear.
I already lost some information this way several times, because I didn't notice this in time.
The webpage was newly opened after the change in the app. When I open the card and then refresh the webpage, the changes remain when editing.
I doen't happen every time, but very disapointing when you lose information.
