I spent a lot of time re-installing .NET, upgrading to 4.5.2, installing hotfixes and nothing seemed to have any impact.
Eventually, I discovered that the following resolved the issue:
- Disable Memory Optimisation that was set in a computer XenApp policy
- Stop and disable the Citrix x64 Memory Optimisation Service and the Citrix Virtual Memory Optimisation Service.
The errors disappeared immediately, without even the need to reboot, and I have received no further calls. Server performance still looks the same so the impact have been zero in those terms. As this is a PVS image, I updated the GPO applied to the targets' OU which stops and disables these services.
Just hoping I can save you a little time should you run into the same issue.