The line in your .bashrc and what you type at the command line are not equivalent. There is a subtle and very important difference, particularly when it comes to setting the environment.

$ /home/db2inst3/sqllib/db2profile
[download]

Will fork a subshell, set the environment (for that subshell), and exit. The environment in your current shell remains unchanged.

Although your .bashrc should be handling it there would seem to be no harm in trying either of these which will run db2profile in your current shell.

$ . /home/db2inst3/sqllib/db2profile
$ source /home/db2inst3/sqllib/db2profile
[download]