Hi,
This appears to be an issue that has been fixed for 7.5.12. You can download the RC from the “early access” section of the downloads. The final should be released within another 2 weeks.
The problem comes from having the same tag defined multiple times in a tag history query. If you can track down where that is happening, you can avoid the issue for now. Otherwise, installing 7.5.12 is the easiest way to go.
Once it starts happening, unfortunately only restarting the gateway will help.
Regards,