I received this bug report in a toot from a Fedidevs user:
Dear @fedidevs
I think there is a bug with the starterpacks: When in “Add accounts” I search for an account that is already in the Pack, the tick-box can show empty. When I click it, it will switch to ticked, but the account is actually removed from the pack. This is also confirmed by the number of accounts in the pack going down.