"but what does it mean when it says "512 requests triggered this suggestion"
It means precisely that, that the "failed to convert character" violation has been seen 512 times during the Learning/Enforcement Readiness Period.
This is a relatively high number of occurrences so its pushing the learning score up each time it sees this violation occur. When it reaches 100% the Automatic Policy Builder will accept the violation into the policy as a required part of the policy in order to allow the application to function correctly.
However, the default behavior for a violation of this type is to Alarm and Block and therefore when this violation type is moved into the Policy and Enforced (as its already in Blocking Mode) any future violations will be Alarmed and Blocked giving you in this case a false positive result.
Automatic Policy Building is great but you do still have to weed out the odd False Positives.