Lessons learned from support cases - common things to look for.
Does DNS function properly?
If not any daemon that's doing name resolution will be very slow.
Does the system have the correct time? Is it synced with a time server?
[nmis@demo var]$ ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
+cachens2.onqnet 13.64.159.31 3 u 426 1024 377 4.845 -0.126 0.458
+ec2-13-54-31-22 54.252.165.245 3 u 352 1024 377 18.036 1.540 1.008
-node01.au.verbn 192.12.19.20 2 u 514 1024 377 18.966 -16.530 1.176
*ntp3.syrahost.c 218.100.43.70 2 u 422 1024 377 63.642 -1.172 0.852
[nmis@demo var]$ date -u
2017. 02. 16. (?) 22:33:31 UTC
Compare the system UTC time with actual UTC time. A site such as https://time.is/UTC will show current UTC time.
If the system time is not correct it will result in a lot of problems.
- Time stamps not correct on events
- Graph data not correct
- Transactions with other systems fail (e.g. cookies could already be expired at the time of issue.)