No, it has never occurred. I've been using it in ecomode for a few months without any problems so that the fan runs quietly. The brightness hardly differs from normal mode.

I have the same phenomenon, Epson simply waffles and says that Ecomode is not intended as a permanent setting, but is used as a reference for the service life of the lamp. Paradoxical.
Perhaps a firmware update that optimises the lamp control and cooling would be helpful, so that the lamp does not suffer any deposits if it is run too cool...this flickering in bright image sequences really drives me crazy.

Yes, I also have this problem sometimes. Everything ran tip-top for about half a year and then it started.
I then switch the projector so that the lamp gets full power and then back again later. Then the problem is usually gone. You can also read about this on forums.