Could be caused by one of several sap sucking/piercing insects such as Capsid bugs. They feed at night and hide elsewhere during day.

I have a limited root pear tree that gets got at every year around this time,or slightly earlier.There is a creature called pear midge. The pears stay smaller and bend over and discolour. Pick them off if you can and squidge the pear under foot. If you split the pear you may see tiny maggots inside. It is recommended to spray at whitebud with Bifenthrin (Hessayon) if you are serious about getting rid of them. Pears are also more fussy about water than apples.