Can propofol infusion syndrome happen from back to back bolus injections? or only from long term high dose continuous infusions?

Only from long term: high dose continuous infusion. It's not called propofol BOLUS syndrome.

Propofol...: Propofol is a strong anesthetic typically used during surgery. It is administered every 10 seconds until onset of anesthesia, total dosage 1 to 2 mg/kg IV. It inhibits the NMDA subtype of glutamate receptors, and has agonistic activity at the GABA A receptor. It can cause respiratory suppression, confusion, hypotension, myocardial infarction, seizures. It can cause these reactions acutely.