Ray,
Thank you so much for this! It seems ordering process is fixed.
The ones who were experiencing this issue are opening sites from bookmarks.
And on their browser other htm pages have this ?COLLCC= after the address as well.
e.g) http://www.rowingcentre.co.uk/index.htm?COLLCC=1627783238&
I should tell them to open the site with proper address after clearing cache, then re-bookmark?
I attached index.htm file as well.