I signed the petition earlier today (hadn’t got round to it earlier) and the same thing happened to me as to your son. The thank you showed that the number had increased but when I went to the actual page the number had not. I see that Jeanette says the number of 38,689 which is exactly the same number which was given to me on the thank you 2 hours ago. But if you go to the actual petition page it still showed 36,688 just now. I noticed there was a feedback option so have sent a message saying my signature wasn’t added, but they say it might take 5 days to get a reply. I wonder how many signatures have been lost. I was going to get others to sign, but think I might wait until they sort it out.
But maybe everyone should check the numbers before and after and if they don’t change send feedback – option at the bottom of the petition page.