what I did was just wait for 10minuets.
when I set a constraint to the Gantt chart, the whole Gant chart misses from the page at first.
but after 10minuets while asking about this issue on this forum and returned to my Gantt chart page, tried to add a constraint again then
I don’t know why but everything turned out to be perfect.
so, wait a few minutes and try again?
hope this will help.