Hello
To sum it up.
- You have no extractors running that is manipulating the data from the input?
- All buffers are 0 so there is no delay in processing data?
- Checked your remote devices and they have the correct TimeZone and the Date/Time is also correct?
- Graylog server Date/Time is correct which matches the remote device, correct?
- The user logged on have the same Time/Zone and the date/Time is correct?
- Did you double check your NTP service and configuration?
- Did you see anything that may pertain to this issue in the log files?
Example:

What I noticed was this.
and this
So you have Linux and Windows going to the same INPUT/ports?
Have you tried to separate them?
Example Linux Servers.

Example Windows Servers

It might not help, but its worth a try. If anything, maybe we can narrow it down.
If you tried and checked our suggestions perhaps something in this post may help.