Lack of flowers on Clematis Montana

I have two large pink clematis Montana at opposite ends of my Cardiff garden which are over 20 years old. Each year they are a mass of flowers - until this year! There are only a handful of flowers on both plants, although there is lots of healthy-looking growth and foliage. They seem to have enjoyed benign neglect in the past, and only get pruned when I have to cut back growth over the path. Any ideas why this year is so different to the others? We've had a mild but very wet winter here - could that be the problem?
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The normal opinion is that it's down to drought, there was an old thread here with a similar problem
https://forum.gardenersworld.com/discussion/1029709/clematis-montana-no-flowers
Maybe it dried out over last summer?
@Fairygirl might be able to help.
Sorry - that wasn't terribly helpful!
I live in west central Scotland - not where that photo is...