Adjusting webcam resolution

I'm running octoprint 1.3.10 on image 4.14.98-v7+ with a Raspberry pi 3B+, my webcam is a Logitech C615. I'm unable to change the webcam resolution. Any change I made in /boot/octopi.txt simply makes the webcam unavailable because of an error, the log says:

Starting up webcamDaemon...
--- Configuration: ----------------------------
camera: usb
usb options: -r 1920x1080 -f 5 -y
raspi options: -fps 10
http options: -w ./www
Explicitly set USB device was found in options: -r 1920x1080 -f 5 -y
Found video devices:
Configured USB camera was not detected, trying again in two minutes

When I check the webcam log, with default parameters, I see:
Running ./mjpg_streamer -o -w ./www -i -r 640x480 -f 10 -d /dev/video0
MJPG Streamer Version: git rev: 821c330ea6bbb5fbed98d48e00aac156e923161b
i: Using V4L2 device.: /dev/video0
i: Desired Resolution: 640 x 480
i: Frames Per Second.: 10
i: Format............: JPEG
i: TV-Norm...........: DEFAULT

Now, I just kill the mjpg thread, cd to /home/pi/mjpg-streamer and run the same command again: this fails.
./mjpg_streamer: invalid option -- 'w'
When I strip the "faulty" arguments:
./mjpg_streamer: invalid option -- 'd'
./mjpg_streamer: invalid option -- 'f'

I already lost a stupid amount of time on this. Anyone can tell me what's going wrong?

Bump. This issue is quite simple, I can't be the only one?

You're not alone I've the same issue with my C910.