Hi

New to group so sorry if this is a regular question

First year with greenhouse

I have a very active cucumber plant in my greenhouse but the cucumbers are
bitter for more than half of their length

I am growing it in a large pot of multipurpose compost with John Innes and
watering regularly

I have regularly removed the male flowers

I have tried picking when fruit is large and smooth and also when a bit
under size and still spikey problem is the same

Recently I had a shop bought one that was bitter for its top third

What am I doing wrong?

I am on the verge of pulling it out to allow more space for my chilli pepper
plants which are doing better than expected

Regards

Tony