Need help figuring out Poe camera issues/troubleshooting

So when i started this job there was like 6 out of the 21 cameras down. 4 where still under warranty so i RMA them and replaced 2. I’ve been doing other projects here over the last 2-3 months and have had over 8 more cameras suddenly stop working and sent in for repair/replacement. Most seem to go down around the time i put a repaired/replaced camera back up then another camera goes down(maybe withing 24hrs). So im wondering how i should go about finding the issue and fixing it.
Some info:

* Sometimes logs will show network connectivity issue then will disconnect and not power back on, and other times camera suddenly disconnects and wont power back on. I always bring them inside and check on other switch to make sure before i RMA them.
 * Most cameras are digital watchdog model:dwc-mb421tir total of 23 cameras.
 * Cameras are mounted to metal storage buildings, server/Poe switches, etc. are surge protected.
 * Most direct burial Ethernet cables are ran underground through conduit(but all conduits are filled with water?, and previous installer didn't use what i would consider "quality" direct burial cable.?)
Thanks for any suggestions

I’d suggest you ask the camera RMA people what they are finding has failed and start to build a list of the common failures etc.

Have you checked the line with a condition test?

specs says " No Fog or Condensation under Any Weather Conditions" which usually means the camera has a lens heater. I’m going to take a guess and say that your cable is 24 gauge and not 23 gauge. I’ve heard camera installers say that the slight added resistance of smaller conductors will cause the cameras to burn out since they draw more power than the standard camera. I heard that early on, so I only run 23 gauge now and haven’t had any issues personally.

Every camera that has went down I have tested the cables and tryed camera on different cable. There hasn’t been any bad cables since I replaced all the ones that tested bad. I will ask them the specific part and try to go from there. I asked them what they thought it could be and didnt really offer to much thought. As far as wire size, the 6 or so cable I have replaced are all cat6 solid copper 23 guage. The rest is pretty much mixed and matched. I was more leaning towards lightning or conduits being full of water but thanks for suggestions I’ll definitely look into them.