Relay CONTACTS will become marginal with time , taking more than one "hit" on closure - the click you may be able to hear.These late model cars have complex systems , antitheft etc. and MULTIPLE relays in "harmony"will be sequentially/in series , needed to actuate - with a good conduction of current.
So find all relays possibly involved in starting and test by tapping with a screwdriver - for "effect". Better yet have some "known good" spares to swap . This would be a start , eliminating your relays , and it's really an easy & clean procedure ??