On 16 Apr 2019, A problem occurred in origin and we can't launch BF4 from battlelog since then.
(edited: they released beta patch to this problem on 24 Apr)
So I'll tell you how to launch from battlelog
First of all, use Internet explorer(this solution will not work with another browser)
Click your icon and go to the setting page.
Then turn off the option named "Use plugin-free game launching" and that's it.
You'll be able to join any servers from now on.(If they ask you to install a plugin, just install it and join again)
Its EAs latest patch that screwed everyone up GLOBALLY. Not just you. U have to launch from the game, until they release a new patch! (DOH)
Yup, I noticed that the latest patch caused the problem and It's not just me. And EA ought to notice this problem.
4 days have passed since this happened, but no patch released after this incident
You can still join from battlelog with this method.
If you use chrome edge or opera, please refer to the link below
https://bf4db.com/forum/thread/battlelog-join-fix-released-3475
It seems to work when using the beta for Origin, they fixed it for now...