I have a strange issue regarding SSL VPN with full tunnel. I had the problem in 5.4.1, I've downgraded to 5.2.8, the same issue.
When connecting to SSL VPN(just from a single user), the whole traffic for that VDOM went dead, the Fortigate stops responding , the traffic does not work from the SSL VPN,the user however remains connected. It's like the Fortigate is not able to encrypt the traffic, it's like is getting overloaded(sometimes I get several ping responds).
When disconnecting from SSL VPN, the traffic works fine. There is an improvement however after the downgrade, the Fortigate responds to ping after the user gets connected, but the traffic is still not working from SSL VPN(the ping works now, but not TCP or UDP).
I've configured the SSL VPN hundred times, not once did I have an issue like this one on a hardware box. The config is correct, opened a ticket as well, I had a support guy look at it, and he couldn't believe it. The ticket is still researching after a week.
There is no patch for human stupidity...