Worklist INSTSTATUS = 1

Is there a generic reason for why Worklist items go to INSTSTATUS = 1?

Scenario: When a Worklist item is created, its INSTSTATUS = 0. Once approved, that status = 2. Occasionally, when the approver goes to their worklist and attempts to approve the item, the approval does not work and the item remains in the Worklist, now with a INSSTATUS = 1. If the user goes back into the Approval and approves again, it will work. The INSTSTATUS will then be 2.

Does this indicate an issue in the workflow or workflow config? Could it simply be a temporary environment glitch that kept the initial approval from completing?