How old are your tires? you stated this:
"Maybe in the rush to install them at the start of the pandemic they didn't get the rims clean?"
Which leads me to believe these were new tires installed in 2020 and are somewhere near 2-3 years old now. Normally this wouldn't be an issue if they were ran regularly but since they have been sitting and not moving, with weight on them for 2 years, and a few of those were underinflated they might be a hazard now. I would have them thoroughly inspected to see if there are any cracks or dry rot and not just on the sidewalls. Tires can develop dry rot cracks in the tread and are harder to see. And there still could be damage you can't see. Weight on an underinflated tire for long periods could damage the belts in the tire.
Hard pill to swallow but your "new" tires might need replacing. Or roll the dice.
I just had 2 blowouts on 3 year old tires. Granted they were cheaper tires but beyond the price of the tires is damage to the RV. And it is taking months to get parts like j wrap to fix it. Luckily the RV is still usable but it's very risky running suspect tires. I don't want to be doom and gloom, but after what I just went through I take the matter pretty seriously.
I have considered that if I need to leave my FW sit for more than 2 months unused I would pull the wheels, put the RV on cribbing and store the wheels/tires in my conditioned garage.
Jeff - 2023 FR Sunseeker 2400B MBS