Excel ran out of resources while attempting to calculate one or more forumulas

I've got a relatively small worksheet (135 kb) giving me a pop up message you see in the title of this post. The message pops up seemingly every time I try to do any operation. Then I get it again if I shut down Excel.

I'm running Office 365, Excel 64 Bit on Windows.

These are the checks and attempts to fix I've already done:

1. Run Error Checking for formulas (none found)
2. Opening a fresh worksheet and copying the bare minimum rows and columns from my original sheet to the new one. Same error on new sheet.
3. Repair Office 365, reboot and try again. Same error. (and there are no circular operations)
4. Cleaning up disk and RAM space. (I've got "free" RAM of roughly 10 GB).
5. Trying to spot problematic formulas, in the event they aren't caught by the error checker.

I'm not using array formulas or pivot tables. Just old-fashioned Excel formulas and function.

I've been using Excel (and prior to that Lotus 1-2-3) for, well... 35 years and have never seen this error message.

My planned solution is to begin deleting columns from right to left, and see if the error stops. But if you happen to know of any bugs or fixes for this feel free to leave a comment!

If necessary I can relabel some of the more sensitive info and upload the sheet just with the formulas, if anyone cares to take on that task.

Thanks!