calendar has lost old entries on iPad
I use iCloud Calendar on my iPhone, iPad and desktop iMac. it has worked perfectly until yesterday. Suddenly, on the iPad - only on the iPad -all entries from more than a month ago have disappeared. Recent entries are still there and new entries sync across all three devices. All entries also are still showing on iMac and iPhone and on the calendar at iCloud.com.
I have tried rebooting the iPad but that does nothing to restore the missing entries.
Any suggestions on how to restore the old entries on the iPad?
iPad Air running iOS 12.4.1
iPhone 6s running iOS 12.4.1
iMac running Mac OS Sierra v 10.12.6
iPad Air Wi-Fi