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So sorry to hear that... :-/
I know how stressful this can be.

Have you tried going to the custom field group that's no longer working, opening your browser's DevTools (Chromium - F12), enabling "Disable cache" in the Network tab, and then refreshing the page?

All "Custom Fields" return this error (but it is not blocking):

deprecated.min.js?ver=e1f84915c5e8ae38964c:2 Bottom margin styles for wp.components.ToggleControl is deprecated since version 6.7 and will be removed in version 7.0. Note: Set the__nextHasNoMarginBottomprop to true to start opting into the new styles, which will become the default in a future version.

The blocking error "Something went wrong. Please try again!" is triggered (in my case) with all "Custom Fields" that contain "Groups" (in version 3.3.2, everything worked normally in version 3.3.1):

i @ deprecated.min.js?ver=e1f84915c5e8ae38964c:2
react-dom.min.js?ver=18.3.1.1:10 ReferenceError: Cannot access 'o' before initialization
    at Module.default (4988.app.js:1:123)
    at c (react.min.js?ver=18.3.1.1:10:2391)
    at Wn (react-dom.min.js?ver=18.3.1.1:10:35439)
    at e (react-dom.min.js?ver=18.3.1.1:10:39675)
    at fr (react-dom.min.js?ver=18.3.1.1:10:54704)
    at hr (react-dom.min.js?ver=18.3.1.1:10:56142)
    at Qs (react-dom.min.js?ver=18.3.1.1:10:123734)
    at wl (react-dom.min.js?ver=18.3.1.1:10:88341)
    at bl (react-dom.min.js?ver=18.3.1.1:10:88269)
    at yl (react-dom.min.js?ver=18.3.1.1:10:88132)
ar @ react-dom.min.js?ver=18.3.1.1:10
react-dom.min.js?ver=18.3.1.1:10 TypeError: Cannot read properties of null (reading 'removeEventListener')
    at A.hasUnsavedChanges (app.js?ver=8c07b96bef0c1b5a19b8:1:243564)
    at Or (react-dom.min.js?ver=18.3.1.1:10:72846)
    at Ir (react-dom.min.js?ver=18.3.1.1:10:73032)
    at El (react-dom.min.js?ver=18.3.1.1:10:92118)
    at fl (react-dom.min.js?ver=18.3.1.1:10:85253)
    at Nn (react-dom.min.js?ver=18.3.1.1:10:32442)
    at react-dom.min.js?ver=18.3.1.1:10:82952
ar @ react-dom.min.js?ver=18.3.1.1:10

However, after fiddling with the console, I realized that the error would disappear on its own when the cache was emptied.

Conclusion: no more React errors when correctly refreshing the problematic Custom Fields pages in the MB Builder.

Hoping it lasts! 😉

Same here with v3.3.2 today. ☠️ 🫠
Thank goodness I made a backup just before.