I hope I'm following correctly - It's quite possible that the picture data in the file is legally scaled (64-940 in 10-bit) but that Resolve is interpreting the file as if it were full-range. Because Resolve works internally in full range, it would NOT scale a file that it thinks is full-range, resulting in the flat look. When you change your monitoring, you are previewing what it would look like if it were scaled.
However, you don't want to make this change in the monitoring section, since your monitor is set up to accept a full-range signal. Try right-clicking on the file in the media pool and changing the "data level." It is probably set to "Auto" but you can manually change it to "legal" or "unscaled." Perhaps one or the other will force Resolve to interpret it the correct way...
And then ensure that you are not clipping - this is assuming that your telecine isn't giving you log or something like that and it's just a levels issue...
KC
Prehistoric Digital