I've had this problem before and it's hard to describe without really getting into it so here goes.
Photoshop has this odd behavior that will automatically select the opacity value in the layers panel and change it based on what you type, even though you have not selected the opacity value. This also happens when clicking to input a value in the properties tab. You know it's going to happen when the text is highlighted WHITE rather than the standard blue. See attached photos for reference.
So for example, I select a layer and click inside the properties tab to change the width. The width number is highlighted WHITE and when I type a number, the opacity of the layer is changed rather than the width. This is super annoying and happens sporadically. Sometimes constantly, sometimes here and there.
I have fixed this before but I don't remember how. I'm running Photoshop CC 19.1.4. I don't have any 3rd party plug-ins. Any suggestions?