Any idea what could cause white, rocky buildup on PoE patch connectors?

Don’t assume it’s harmless dust. Moisture-related corrosion or mineral residue is one possibility, even if there isn’t a visible leak beside the rack. Check the cable routes from end to end, especially any outdoor runs or penetrations, and look for dampness, damaged jackets, or residue inside the plugs and jacks.

Since the deposits are interfering with the connection, I’d take the affected ports out of service and replace the contaminated patch panel or jacks rather than just scraping them clean. Also inspect the switch ports and cable ends before reconnecting, and keep an eye on whether the residue returns.

Plastic blooming or weeping is another plausible explanation, particularly if the material is appearing on the panel’s plastic and the rack stays warm. Some compounds can migrate to the surface, leaving a tacky or crusty residue. That would fit better if the metal contacts and cable ends look clean.

Cleaning may remove what’s there, but it won’t fix a panel that keeps producing residue. I’d document which ports are affected, check whether the panel itself is warm, and plan to replace it if the buildup comes back. Avoid solvents unless the manufacturer says they’re safe for that plastic.

PoE by itself doesn’t tell you what the deposit is. The useful clue is whether it’s only on the panel’s plastic, or also on the contacts, cable plugs, and inside the cable jackets. Inspect a few affected and unaffected connections side by side, and note the room temperature and humidity. If you can, check the same cables at the far end too.

If the material is on electrical contacts, or connections are becoming unreliable, don’t rely on cleaning alone. Replace affected parts and investigate moisture or contamination along the cable path. The appearance in a description isn’t enough to identify the substance confidently.

Short version: replace the patch panel if the crust is physically ejecting plugs. Picking deposits off might restore a connection briefly, but it won’t explain why they formed or prevent them returning. Before installing a new one, inspect the cable ends and switch ports so you don’t carry contamination over.