Using an old, manually installed version of Hive Keychain seems to be the #1 culprit. If it's up to date, check that the API node it is using is in good shape and change if necessary. If using Peaklock, try switching to a known-good node. Also apparently Brave does not automatically update browser add-ons, so with Brave you should update Keychain manually.

Find a good node using one or both of these sites:
https://hive.ausbit.dev
https://hivekings.com/nodes

Credit goes to @crimsonclad for this info ❤️