The difference that matters
A task is planned work, part of the project's normal delivery. An issue is a reported problem, from the client or the team, that wasn't part of the initial plan.
Why they get mixed up in practice
Without a clear rule, a problem reported by a client can get logged as a task, losing the "reported by whom, when, with what evidence" context that an issue naturally preserves.
A simple rule
If it comes in as a request planned from the start, it's a task. If it comes in as an unexpected problem that arose along the way, it's an issue. Applied consistently, this rule removes the confusion quickly.
Bottom line
Clearly separating tasks from issues isn't bureaucracy, it keeps visible what was planned versus what came up unexpectedly, useful information at any project retrospective.