When I export a photo to windows as a jpeg, the file size is always reduced by about 95%. for example a 20 MB file becomes about 1 MB, even I made no adjustments to the original file. I never had this problem with previous version of lightroom.
I am using PEF, but when I went into export settings I saw that the file quality was set at a 60% value instead of the 100% I normally use. I have two versions of Lightroom and this was part of the new Adobe Cloud and a newer version on a newer computer. I had forgotten that it still had the default setting.
Thanks for your quick reply, it made realize what was wrong.