In recent DB2LUW levels a common reason why force application might not work

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Force application is not being  able to force certain applications.

This was not uncommon in older levels of Db2.

When a force application is issued against a specific application an interrupt is sent to the specific session code to gracefully  terminate the session.

However, there were code areas were the  needed interrupt handling  were missing.

Over the time the db2 codes have incorporated those interrupt handling which allowed a  session to gracefully go away.

However, in the very recent Db2 levels  a different kind of  force application hanging is being observed.

Over the time the  Db2's  capability of handling certain kind of traps have been improved.

Db2  have become much better isolating some specific problem thread and suspending it successfully  avoiding a  full blown Db2 instance crashing situation.   The  reason of those suspended threads  are to be diagnosed and cause to be found out  with the help of IBM Db2 Support.

As  an end customer  many times those suspended threads are not even noticed  unless looked into the db2diag.log.

Messages like following  could be observed,

2018-06-05-14.39.18.476000-300 E28753113F502        LEVEL: Severe
PID     : 3988                 TID : 285355         PROC : db2syscs.exe
INSTANCE: DB2                  NODE : 000           DB   : MYDB
APPHDL  : 0-43733              APPID: <>
AUTHID  : MYID             HOSTNAME: MYHOST
EDUID   : 285388               EDUNAME: db2agent (MYDB) 0 (suspended)
FUNCTION: DB2 UDB, RAS/PD component, pdSuspendEDU, probe:10
MESSAGE : EDU has been suspended

Above  messages will have associated dump files  before that in the db2diag.log

As the end users  might not even notice that some of the sessions are in suspended state they try to force related application  which will not work as the associated thread is in a suspended state.   No logical  interrupt  will reach to a suspended thread.

Only an instance recycle is needed to cleanup those suspended threads.

So, if a force application does not work then it's suggested to check in the db2diag.log if anything is being  suspended  or,  not.

If  anything is suspended  most  likely  it will be a code defect or,  effect of any other issues.

So,  instead of  focusing on why a force application did not work it will be suggested  to call the IBM Support and share the details  to find the issue.