I manually installed Mastadon on a Digital Ocean 1Gb droplet (unrelated to Cloudron), and with only 1 user and 5 posts, it ran out of memory. I bumped the droplet up to the 2Gb option and it ran smoothly.

@girish Yes, that did the trick - thank you so much! The package version 1.1.1 works for upgrading to Mastodon 3.1.2. Thank you for resolving that so quickly.