Common Reasons Price Rules can deliver unexpected results

1. You have a Price Rule based on one of the Total Fields on the Quote Line

The Out-of-the-Box total fields on the Quote Line are formulas that are based upon their respective Unit Prices. The unit prices for these are not calculated until the native part of the calculation sequence, and these formulas are not recalculated until after every Price Rule event has taken place, meaning there is no point at which you can reference them in a Price Rule and have them run without calculating multiple times.

2. You have a Price Rule running On Initialization that references a formula field on the Quote Line

Formulas are not first calculated on the Quote Line until immediately after the On Initialization event, meaning you cannot reference them until Before Calculate at the earliest.

3. You have a field dependent upon the SBQQ__RequiredBy__c lookup on the Quote Line

The Required By lookup is a lookup to the Quote Line object. On the advanced calculator, no records are inserted into the database until the Save event happens, meaning these relationships don't exist, and you cannot reference anything on these until after Saving.

4. You have a Price Rule that depends on fields present on the Block Price or Discount Tier lookup fields on the Quote Line

This is similar to 1), but Related Records are not loaded between the native calculation sequence (which picks the tier/price applicable to this line) and the After Calculate event, which means that no Price Rule can access values on these records until the line is calculated once more.