Forticlient drops immediately after connection on specific network?

[airjn]

Hello! The issue I'm seeing is that FortiClient will connect from the my home network, but the connection drops immediately.  sslvpn.log says this:

20250829 10:08:18.570 TZ=-0400 [sslvpn:DEBG] vpn_connection:3447 Start IO loop
20250829 10:08:18.573 TZ=-0400 [sslvpn:INFO] main:1781 State: Connected
20250829 10:08:18.605 TZ=-0400 [sslvpn:EROR] vpn_connection:1316 IO write remote failed. SSL error: 5
20250829 10:08:18.605 TZ=-0400 [sslvpn:EROR] vpn_connection:2290 Error: Disconnected because of error: IO write remote failed.

The odd part was I went to random public wifi hotspots...and it was able to sustain a connection. Forticlient on other computers (windows though, don't have another linux one) didn't have a problem from this network. It did work for several months before this issue happened, so it doesn't seem to be something with the network.  

I was able to get it to connect once by changing the IP range of the network, i.e. what the DHCP handed out. (192.168.x.x to 10.x.x.x).  The issue came back after the next restart however. 

Setup: Ubuntu 22.0.4, says "full tunnel" in the log, not network restriction, I think it's ZTNA.  RSA token auth. Has EMS.  FortiClient 7.4.3.1736 (it upgrades it's self pretty often). 

It's similar to this but there was no solution there. 
The sslvpn.log has this:

20250828 17:32:31.649 TZ=-0400 [sslvpn:DEBG] vpn_util:299 List fctvpn connection: fctvpn7e272de6
Galaxy A71 5G Network
GW Guest Internet
Havoc82-5GHz
IHOP Secure
lemondrop
McDonalds Free WiFi
MPL
minnow006-hotspot
minnow014-hotspot
ORBI62-Guest
LISI
LISI-5G
SSG-B
Vat_Guest
Verizon-R200L1_6F
Wired connection 1
Wired connection 2
Wired connection 3

Which seems to be list of networks that have been connected to, i.e. there is some sort of cache. It also seems like that cache got corrupted somehow.

Is there some way of clearing the list "seen networks", as it seems to work fine if they are new, till it matches them with an existing one at least.

Anyone know a way of clearing that list short of wiping all the user data (which would probably require re-registering somehow)

[tbarua]

Hi, 

Have you tried upgrading the FortiClient if it's an old version? 

[airjn]

Doh! I should have mentioned that(fixed!).  It's 7.4.3.1736 currently. (re-installed last week) and it self-upgrades pretty often.