After updating to version 17.5 my customized settings such as: heuristic sensitivity, packers type, PUP scanning, and exclusions setting are reset to default.
It will be nice if in the future, the new version automatically detects my settings and leaves them intact.
It should leave your settings alone, but it does rather depend on how you install the update and possibly what or how old a version the existing installation was.
If you do a clean install then it wouldn't. I don't know if you allow the avast program update to Auto Update, I believe it should retain the settings, but I have
'never' allowed it to do that so I can't speak from personal experience.
An update from the existing avastUI should retain the settings, if you downloaded the full off-line installation setup file and install that over the top of the existing installation, it should retain the settings. That is what I have just done and it has retained my settings.
The above is what should happen.
Note: before a program update I always do a hard drive image, should I ever need to go back.
If that is too much, then the least I would recommend is to backup your settings, avastUI > Settings > General - scroll down to the 'Back up settings option. You can then restore them should it be necessary.