Hmmm… I am still not able to replicate this random behavior on your site.
I added another 5 tests, saved. All were added. Then added an additional 3 tests and those were added. Then I delete the last 3 added and added 3 new tests and saved. Then followed up with other random changes saving in between and they always worked as expected.
Your browser or local firewall, perhaps??? I don’t know All Ic ansay, not matter what I do it seems to work.
Do you have more date types to add? If so, what are they so I can add them to see if it has to do something with your chosen labels. (I did test randlon labels like existing one and they saved fine too.)