What's going on with my setup?

remove the script

sudo bash -c "$(wget -nv -O - https://github.com/wiedehopf/adsb-scripts/raw/master/autogain-remove.sh)"

Then adjust the gain

Setting the gain manually,it depends if you have the package installation or working with the SD card image installation

Automatic gain can be usefull but that might be to high to your liking.
Set the gain manually and wait 24 hrs to see if there is an improvement or a decline in your reception.
Don’t expect wonders, autogain checks once per hour to see if the value is still correct but it seems to be quite steady in your set-up.

Don’t you see any aircraft with the filter added ? It seems it filters out some noise in your graphs but the noise figure is already low

Supported gain values (29):
0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6

For the package installation

sudo nano /etc/default/dump1090-fa

Scroll down and change these two lines

RECEIVER_GAIN=60 → Change this figure to to the number you want
ADAPTIVE_DYNAMIC_RANGE=yes → Change yes to no

then restart dump1090-fa

sudo systemctl restart dump1090-fa

For the SD card image

sudo piaware-config adaptive-dynamic-range no

sudo piaware-config rtlsdr-gain (number you want to set)

sudo systemctl restart piaware

sudo systemctl restart dump1090-fa