I think it has been going on for a year or more. My Hertz rentals seemed to go more smoothly and could count on better vehicles or easier resolutions to the rare issue several years ago, before ever hitting Five Star status. After hitting Five Star and then President's Circle last year, things seem to be continuing to get worse.

I routinely have minor issues (contract says full tank but it isn't, car isn't ready at reservation time, charged a drop fee even for a RT rental, etc.) and bigger issues such as no vehicles available or one car that literally had a pile of ashes on the back seat, with no other vehicles or an offer to do anything other than "making a note of it." That confirmed one-class upgrade seems to rarely happen, and even when it does the vehicles seem to have 30,000+ miles.

I think quite a bit of this is due to extending status to Delta and United elites (plus co-branded UA Chase card holders) but I think there has likely been a shift in management philosophy and strategy. Staffing seems minimal at most locations and people just don't seem to take pride in their work. I will say that for the most egregious problems I have encountered, I have been able to contact someone and Hertz has tried to maker things right -- but I have also shifted the bulk of my rentals to National where things seem to run more smoothly, upgrades are honored, and vehicles are generally newer and cleaner. The downside to that is that National lacks the number of HLE locations, but you can always use Enterprise to accrue Emerald Club credits.

National also has a status match program: https://statusmatch.emeraldclub.com/usen/

I will probably still hit Five Star with Hertz this year (since it's only seven rentals) but National has kept me as a generally happy and returning customer. I actually had a Hertz rental last week (good location and a super low rate) without any major issues, but the car was a 30,000 mile vehicle that smelled like smoke, had significant scratching, and of course the upgrade wasn't honored so I was reminded of why I generally prefer National