Nether portal does not work

I have to log in and out like 4 times before I can travel through the netherportals (i have traveled with before). 
it was hard to add a long enough video since there is a restriction of 10 mb. But i used the same portals before and it used to work but now it only works after lots of tryies

 

i think my version is 1.20, at least since now 15:15 ( 26th of april) it isnup to date