This is caused by a build up of Ajax Requests causing the Seam conversation to timeout. You've already included some flood control in your ajax request (ignoreDups, eventsQueue and requestDelay), but you can still optimise it further:
- Firstly increase the value of concurrent-request-timeout to something much higher than the default (is it 500?): eg. mine is 10000
- Secondly you could use the minChars attribute of the suggestionBox to limit the size of the resulting query from the server. I have mine set to 2 as my result set is potentially 20,000. Makes sense to limit it.
- Thirdly, is your suggestion query optimised? eg. DB table is indexed appropriately etc.
And have a look at this JIRA