GFI: Potentially irritating behaviour in feature list

Describe the bug

The GFI's feature list will, on high zoom levels, at times display a feature list with a single entry, despite a blue multi-marker indicating multiple features is present. This is confusing to users, as they only see one entry, but apparently multiple features in the map.

This results of blue multi-markers resulting from active and inactive features combined, but the feature list will only display active features.

Expected behavior

We just don't know. We have no idea how to resolve this properly. We also don't remember why isSelectable is a feature at all.

Steps to reproduce

1. Zoom in and pan around until you find a multi-marker that has but one feature list entry

Screenshots

Desktop

Any

Smartphone

Any

Additional context

This issue stems from the discussion in https://github.com/Dataport/polar/pull/447#discussion_r3713393641; we continued it by ☎️, but didn't come to conclusive results. It does not matter practically at the time being, but is kept as an issue for future rework.

Start by reviewing the feature-list and multi-marker behavior described in the issue, then read the linked pull request discussion about isSelectable. Reproduce the case by zooming and panning until a blue multi-marker has one visible feature-list entry. Done means the team has agreed on the intended behavior and the list and marker state are no longer confusingly inconsistent.