I just tested it on 8887 and preloading works for me.
Can you please provide more information regarding why you believe pre-loading is not working?
Any errors, screenshots to share more details.
The error SQL message is trying to state that the operator with ID 3430 does not have read access to the folder where recipient with ID <you have hidden in BLUE>. Please check the rights of operator 3430 which I believe is operator "webapp" or could be something else in your case and assign the rights accordingly.