Found below issues : -
1) Drools max limit exceeding when two or more promotions are stackable and rule group is null
PRM_1 config.- rule-group=null; priority=1; stackable=false; condition= cart-total>$100 ; action=fixed discount of $1
PRM_2 config- rule-group=null; priority=1; stackable=false; condition= qualifying-product=1934406) ; action=fixed discount of $1
These promotions are not getting applied. getting following error Logs: ERROR [hybrisHTTP12] [DefaultCommerceRuleEngineService] Possible rule-loop detected. Maximum allowed rule matches has been exceeded. Current Limit:200 201:13953159-0ac2-40d4-90c4-4fa22b4e1298 199:7169b4d7-bace-408d-81a3-42ddfa7aa95d You can adjust or disable the limit for rule matches by changing the ruleFiringLimit field in the 'Drools Engine Context' object (see the 'Rule Firing Limit' attribute).
2) In previous version(6.2 and 6.4), promotions present is different rule groups were getting fired(irrespective of the stackibility flag). But, in hybris V6.6 when two promotion are in different rule-groups and stackibility is false, then, only one promotion with the higher gets applied.