Error when trying to categorize cards under option 1 (hardest to remember)

[NameLessGO]

Anki error for older cards only when lapsing

Updating to the latest Anki version should fix it.

As the moment im writing, 2.1.60 is the latest release → Releases · ankitects/anki · GitHub (Recommended)

Alternately, here is another solution

Unable to use "again" button on MacBook Pro

Couldn’t find a solution to this problem, could you try Anki → Preferences → Scheduling → V3 Scheduler Hopefully by using the v3 schedule it will avoid the v2 schedule error if you use anki mobile, you will need to enable v3 schedule on anki droid, v3 schedule is available on alpha builds AnkiDroid 2.15 User Manual