Commands

One command, and it runs entirely on your client — it is never sent to the server, so it works everywhere, including on servers where you have no permissions at all.

/raidicons

Reports what the mod can currently see. Run it while aiming at a raid den crystal: the most useful line it prints is what the game says that block actually is.

Raid Icons
  den block: cobblemonraiddens:raid_crystal_block
  layers: minimap=true worldmap=true
  scan: 4096 chunks examined, 3 den(s) known
  nearest den: fighting tier 5 at 214, 71, -388 (36m) boss=klinklang_terafighting
  looking at: cobblemonraiddens:raid_crystal_block [raid_type=fighting, raid_tier=tier_five,
    is_active=true] - MATCHES the den block

Every line answers a different question, and together they narrow any "my dens aren't showing up" to one cause:

Line	What it tells you
den block	Whether Raid Dens is installed at all. NOT in the registry means nothing can ever be found.
layers	Whether Xaero's minimap and world map were found. Both false means the mod has nowhere to draw.
scan	How much ground has been covered and how many dens are known. 0 chunks examined means the scan is not running.
nearest den	The closest den the mod knows, with its type, tier, distance and boss.
looking at	The aimed block's registry id and every blockstate property it carries, verbatim — and whether the mod recognises it.

The report also goes to your log (logs/latest.log), so you can read it afterwards, or paste it into a bug report without having taken a screenshot at the right moment.

The line that matters

Everything this mod does rests on one assumption: that the crystal in front of you is the block and the properties it expects. looking at confirms or destroys that assumption in one step. If it says is NOT the den block while you are aiming at a den, that is the whole bug report.