I've been fighting this as well.

Here's my situation, the easiest possible match:

• Two bank checking accounts at the same bank
• Transfer from one to the other
• Each transaction is on the exact same date for the exact same amount
• Each transaction has the EXACT same Memo line
  • WEB TRANSFER (3287078) FROM x1129 TO x1520
  • The number in parenthesis is a unique number for every transaction and is identical in both transactions in QBO
• Sometimes, it finds the match; sometimes, it doesn't.  There is literally no difference between the two transactions that it handles differently.

I've attached an image showing 1 transaction that's paired and the rest that have a rule applied (yes, it does the same when the rule isn't active).

This is probably the most ridiculous, frustrating and undata related issue I face and we do big data.

Side note:  Everyone reading this, make sure you actually do the survey it pops up and asks you to do