lilac and laburnum

My lilac trees were absolutely laden with the most intoxicating blossom last year. This year one small patch on one tree none on the other can anyone explain/ Similarly my laburnum dripping with blossom last year zilch this!!

Likewise with my lilac tree, no idea why.

I was told years ago that one in every 4 years a lilac tree has a bit of a rest. Not sure how true that is, or whether it's an old wives tale!

Thanks for that I wondered if it was something to do with the weird weather we've had re hot dry March followed by total washout!! Thou I have seen lots of lush laburnums in the neighbourhood