I was adding some code to the On Success property of a form that already had a fair amount of code in it. When I clicked the Format text button to apply formatting I suddenly got an error on that property. I then noticed that 2 of the four Flow calls that I have on that property were missing, with only the Run() remaining. I restored a previous version to get the calls back and tried adding the new code again with the same result. I ended up just having to copy the flow calls before adding the code and then pasting them back in after they got deleted, but this is obviously not good behavior.
In case it helps the original code and the new code are attached. You can find the missing flow calls by searching for Run. The only difference I can see between the calls that got deleted and the ones that didn't are that the ones that got deleted didn't have any parameters.