Screen stops refreshing after some idle time

Terminals in question are 5010s, yes they are old but still is decent kit for 2D environments. Users log in to Citrix workspace from it, connect to their virtual desktops then do nothing on them except watching screen. No issues for some time, then screen content stops refreshing, i.e. it says frozen until some interactive input is provided, like mouse move or key stroke. It is far from ideal for users watching live, quickly changing data. Is there any setting to disable such behaviour? I can't find anything relevant in documentation. Screensaver is disabled obviously, both Windows and WYSE box side.