We have upgraded to 1.7.7.5 about 12 months ago, and have been adding items slowly to our website. Received the error unable to update settings, Just did a few testing, some new items that we just added we can update description, add photos, update quantity etc. While most items we can't.
I have cleared back end cache, cache/cookies on browser, went into Performance enabled css cache, js cache, smarty cache etc nothing changed, I have updated php version from 7.2 to 7.3 no fix. Disabled all non prestashop modules, disabled all over rides nothing changed.
Recent changes was Reconfiguring the USPS/UPS Shipping modules by Webkul last Thursday, no other changes, we have been adding quantity everyday so not sure it's related to the shipping modules.