If you suddenly experience intermittend problems with your ICA Session performance monitor counter you might just have installed a hotfix without reading its description. Luckily this is not a one way to hell as you can recreate your counters as follows.
After you have progressed this one you should always export the registry key holding the necessary registry data before you apply any hotfix and import it afterwards.
If you do have a certified Citrix Solution Advisor with you he might be so nice to provide you and help implement the necessary limited fix to eliminate this issue once and for all.
vor 2 Monaten