AZ most of the plumbing now is all plastic, plastic is OK, we use Pex in home building these days, there is however a wide range of fittings and quality, some of the RV stuff I have seen has been pretty cheap, fittings can fail, more often than not it happens during the original install, (over tighten, bend aggressively, etc....) it holds for awhile but after traveling and use it ultimately fails. Don't get me wrong it could have frozen due to remaining water, but you did use a compressor, and hopefully opened your low point drain and bypassed your water heater. If you must change the whole fitting use a higher quality one......good luck.