I would be checking your device stats on the backend gw for the devices in question from where your tags are coming from, as well as the tag group settings they're part of in the backend gw(as already mentioned). If your PLC is overloaded, then this could well be the reason you're not seeing fast tag updates. This is under Status -> Connection: Devices. Then click on your device's Details.
Note, the fastest rate that remote tag providers will be delivered tag value updates is 1s. I don't believe this is configurable: Remote Tag Provider updates tags slower than Realtime Tag Provider - #2 by Kevin.Herron
The frontend won't have any (relevant) tag groups if the tags are coming from the backend