As stated befor this is lag realted. It happens to everyone at least once and those (puts on fire resist and prot) with crappy CPU/connections more than most. This isn't a software issue but a hard ware issue.....yours to be exact. It happens to all of us.
Just because you base save is below 24 doesnt mean you cant make the save. Anbody can make it by getting a 20 (auto-save) or byhaving a total save (base + roll) of 24. It works properly.