FortiGate randomly drops VPN connections without any clear reason

[Rovmenpaul]

Hi all,

I’m facing a frustrating issue with my FortiGate firewall. Remote users are getting disconnected from the VPN randomly throughout the day. There’s no pattern to when it happens sometimes within 10 minutes, sometimes after an hour and the users have to reconnect manually each time.

We’re using SSL VPN, and everything looks fine in the logs. Bandwidth is stable, and there are no clear errors reported when the connection drops. The same users are reporting it across different ISPs and devices, so I don’t think it’s just on their end.

I’ve checked timeout settings and session TTLs, and nothing seems off. At this point, I’m just looking for any angle — even reviewing small details like session behavior, logging anomalies, or traffic patterns. Sometimes, looking at the issue through a fresh lens (like categorizing by nouns that start with A — activity, authentication, allocation) helps uncover something you’ve overlooked.

Thanks in advance for any help.

[fg_muc]

Hi,

could you share some background info on your firmware versions of the FGT and FCT?
I have seen some issues in the past with FortiClient 7.4.3 where connections crashed.

[filiaks1]

Except what @fg_muc  mentioned have you checked the forticlient vpn.log file or enabled extended debug. See How to enable debug log in FortiClient - Fortinet Community 

If you don't see the issue then SSL VPN Troubleshooting - Fortinet Community / FortiGate debug SSL VPN daemon - Fortinet CommunityFortiGate debug SSL VPN daemon - Fortinet Community you may need to debug outside working hours.

[adhawan]

You may find the following article helpful in this instance as it specifically refers to the issues and some methods to deal with it:

https://community.fortinet.com/t5/FortiGate/Troubleshooting-Tip-Possible-reasons-for-FortiClient-SSL...