The database may be taking a long time to respond to DE (dSeries) updates and selects. Check for following messages in the tracelogs. Normally, wait times should be few seconds to few minutes for most applications. If the wait times are constantly going to over 10-20 minutes to a few hours, then DB is taking a long time to respond.
Waiting time was 31 minutes 2.590 seconds
Waiting time was 43 minutes 36.256 seconds
Waiting time was 18 minutes 1.201 seconds
Waiting time was 4 hours 38 minutes 37.396 seconds