All CartThrob settings screens are white screened

Question

About a month I was working on a client site and was able to access and edit all of the CartThrob settings screens, including Shipping, Taxes, and Payments. Now, as of last week, whenever I try to access any of them they are all white screens. No changes were made to system files in that time (i.e. no commits to the repo).

I have turned on all debugging with no results and upgraded all the plugins and extensions that I can with no change.

This was originally on an EE 2.7.2 platform, so I tried a direct upgrade to the latest 2.9.0 and was completely unable to access the control panel due to the following error: An Error Was Encountered. Unable to load the requested class: services_json Unable to resolve that issue I reverted back to 2.7.2 and tried the next sequential update to 2.7.3. That update worked but the CartThrob settings pages are still white screened. I've emailed EllisLab to request the install files for 2.8.0 to try the next sequential update.

I can't find any reference to conflicts between CartThrob and another extension but maybe someone here has come across something before. Here's a list of current modules:

Extensions:

and Plugins:

Answer 1

It turns out I missed the devot:ee Monitor accessory, and in looking to upgrade that one came across this blog post from devot:ee that Monitor has been retired.

As soon as that was uninstalled, I was again able to access CartThrob.

It seems like there should be a better, faster way to determine which extensions are causing conflicts. Is this something that should be integrated in each extension (in this case, CartThrob) or in EE itself?