RDS Session Hosts sometimes need a scheduled reboot. Its been the same for years, even with Citrix so in order to do this just create a custom Scheduled Task.
Open Task Scheduler.
Click Create Task on the right hand side.
Give it a name that will easily identify what the task is doing and change the User or Group to BUILTIN\Users then click OK.
Click the Trigger tab and click New and schedule the reboot that is relevant to your environment. Click OK once configured.
Click the Action tab and click new and ensure the Start a Program option is selected for the action and type c:\Windows\System32\Shutdown /r /f /t 600
The options at the end are /r (restart) /f (force) /t 600 (time of 600 seconds. Amend these as you see fit.
Do this for each of your RDS Session Hosts. Or alternatively you could create a Group Policy preference and attach it to the OU in AD that contains all of your Session Hosts instead.