Oxy can also permanently damage chips, worse than ultrasonic. It can bleach colors (some much worse than others) which can't be fixed or restored by oiling. Excessive heat, incorrect concentations, and excessive soak times can all be culprits -- and all vary by chip type/mfg and color. There is no single one-best-way-fits-all.
There are literally dozens of different cleaning methods, using different products and processes -- and every single one of them has drawbacks.
When the casino-used primary PCAs were first introduced, they introduced new levels of nastiness (and some of the Empress Casino chips that followed shortly afterwards weren't far behind). Cleaning methods that had worked well before were found to be seriously lacking and ineffective, and/or far too time-consuming.
Taking chip geekiness to new levels, I was part of a cleaning products study group and controlled experiment, which compared the results of a wide variety of cleaning solutions which had been discussed and used on clay chips at the time: Dawn Dish Soap, Oxyclean, Resolve Carpet Cleaner, Resolve Upholstery Cleaner, Simple Green, several different automotive tire/rim cleaners, even some alcohol-based and ammonia-based cleaners. We tested kitchen products (dish, dishwasher, oven, and general cleaners), laundry products, automotive cleaners for various surfaces/materials, and industrial degreasers.
Nothing cleaned better or quicker without damage than oxy, Resolve, or tire cleaner (three-way tie), although the latter two took a bit longer (by <10% or so) but also never inflicted any damage whatsoever (unlike oxy). But they were more expensive and nastier to deal with, and some left a 'cleaning solution' smell afterwards that eventually faded away.
As a result of all the testing and results,
I used Resolve for a long time, eventually replacing it with oxy solution (but testing thoroughly on each chip type/color before large-scale use, to avoid color-bleaching and hot-stamp damage).
I finally got smart and settled on just buying clean mint chips.
These days, I use either oxy or an ultrasonic for those rare occasions when I need to clean chips, pending the number involved.
There is no universal 'right' way to clean chips, but there sure are a lot of wrong ways.