I don't know if this is of any help:
It happened to me a couple of times until I learned what was causing the reset.
In one of my setups I am using a switchable power strip.
If I turn the power strip on and immediately press the encoder to turn on the DL200 , the settings are reset to defaults, also volume settings. I have to wait a few seconds before I press the encoder to prevent the reset.
I noticed the changed settings because I usually use the auto-display-off feature and suddenly the display stayed on.
Just change a setting, for example select filter FL7 and try my procedure or your procedure by holding the encoder and turn the DL200 on. The filter FL2 should be the default.
Another procedure might work to initiate a factory reset:
Turn the DL200 on by pressing the encoder.
Disconnect the power cord.
Hold the encoder and connect the power cord again.
If the DL200 was on when disconnected from power it automatically turns on as soon as it gets power again. By holding the encoder it might initiate a factory reset.
Please let us know what works.