Mark Allread wrote:

Having defrosted the freezer I have found that a number of the plastic
trays have developed cracks in them.

Check the type of plastic, usually marked with a triangle and number or
letters

https://upload.wikimedia.org/wikipedia/commons/c/cd/RIC_Updated.jpg

Get a suitable glue for that type of plastic. Leave the trays out to
warm up and dry off before gluing, has given me good results.