Do you have something set up in your "Task Scheduler"?
Do you have any external storag? USB stick?
Have you tried clicking on Recycle Bin Properties which has the setting to directly delete files? I would have thought you would have noticed if nothing ever appeared in the Recycle Bin. You can set each drive separately so it is possible one drive is different to the others if you did not use the global option.
At this point you will have to do a lot of digging yourself.
You did not respond to Powerpack's suggestion of deliberately putting a file in the bin and rebooting immediately to see if it is deleted. That makes sure no other apps are coming in to play prior to reboot.
When the PC reboots you could also try refreshing the Bin and Undo Delete if that option is available.
It's most likely a task, a macro, a cleaning program, an optimizing program that is the issue. You may not be aware it is running on startup as some work in the background. There are a number of utilities that can list all startup items. Safer Networking's RunAlyzer is one (example only). You may have to work all the way through the lists.
Look through your list of Start / Programs to jog your memory of what is installed.
It was there after reboot but then disappeared? Are you referring to how long the reboot took?.....It took a while but it's no longer there.
It was there after reboot but then disappeared? Are you referring to how long the reboot took?
Start up Task Manager as soon as possible after reboot and see which processes are running, including any that run and disappear.
I don't know of any programs that produce a simple list of processes as they run. All the utilities from SysInternals are going to give a list thousands of items long during reboot so would have limited use.
You should add all your malware programs into the list of potential problem apps. Check the settings.
The listing after it's started is not what I was suggesting. If you have an app that is fleeting during startup, it won't be on the list at the end. You have to observe what starts, and what disappears as it happens.
However, my post #11 about CCleaner was dismissed because you haven't run it. There it is in Task Manager. Re-asking the question:
Running CCleaner or similar on startup with "Empty Recycle Bin" selected?