Did you drag all of your tags from the PLC into Ignition? If so, you screwed up. Only make tags in Ignition for the tasks you need Ignition to perform.
Meanwhile, some reading for you:
Read all of the linked topics, too.
In particular, look at the Msg Class 3 stats in your PLC's diagnostic web page. If you've maxed that out, your problem is too many tags for your PLC, or too many too quickly for your PLC.
FWIW, 250ms scan classes are unusual in SCADA applications.