You can try this
Do a "get socket"
and then clear the stuck connection by "clear socket id "socket value"
In the example below I want to clear a telnet session. Socket number 122 has telnet open.
fw01-> get socket
Socket Type State Remote IP Port Local IP Port
0 tcp close 0.0.0.0 0 0.0.0.0 0
1 tcp4/6 listen :: 0 :: 443
2 tcp4/6 listen :: 0 :: 23
3 tcp4/6 listen :: 0 :: 22
12 tcp close 0.0.0.0 0 0.0.0.0 0
14 tcp4/6 listen :: 0 :: 6969
70 tcp open 10.1.1.1 1468 10.1.1.2 1114
89 tcp close 0.0.0.0 0 0.0.0.0 0
90 tcp close 0.0.0.0 0 0.0.0.0 0
91 tcp close 0.0.0.0 0 0.0.0.0 0
122 tcp open 172.2.2.2 4857 172.3.3.3 23
205 tcp open 10.16.1.1 7800 10.16.1.2 1145
256 udp4/6 open :: 0 :: 500
257 udp4/6 open :: 0 :: 4500
258 udp4/6 open :: 0 :: 500
259 udp4/6 open :: 0 :: 4500
260 udp open 0.0.0.0 0 0.0.0.0 161
261 udp open 0.0.0.0 0 0.0.0.0 0
276 udp open 0.0.0.0 0 0.0.0.0 0
fw01-> clear socket id 122