I got some pings for updating #mastodon to 2.6.1 from 2.5.2 on #yunohost
I have fixed it for myself on dev branch. It has worked for me, but not work for you so please backup before trying it.
How to upgrade?
$ yunohost app upgrade -u https://github.com/YunoHost-Apps/mastodon_ynh/tree/develop mastodon --debug
mast.datamol.org is one server in the network