I know that home water heaters do much the same thing when they get old and have an excessive sentiment buildup inside the tank. Perhaps you've been camping in a campground that has very hard water and your tank is limed up.
Days camping (2016)----181 days
Days camping (2017) --- 82 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi, w/air suspension
30 years RV'ing
11 different RV's