I've been working on a poster for a play that will be going on in my community in the next few months. Everything was running smoothly until at one point the opacity was far less than what was required on the text I needed. I checked the opacity slide and it said it was at 100%. I tried a different text box with a default font-thinking it might be an error in the downloaded font-but I had the same result. I then tested to see if it was only the text tool by drawing several squares but those all appeared translucent as well. One of the most baffling things, if I moved one of the falsely transparent objects over another with the same glitch, the object beneath would not show. For example, in the image below, the teal square seems to cover "Queen of the Desert" but it acts as a transparent object where it covers the camper. The text and square are the only pieces acting like this. All other elements were created before this problem arose. I think the form of inkscape I'm using may be out of date, but I'd rather fix the issue in this edition than have to completely uninstall and redownload the program. Does anyone have any solutions to offer?

It would be great if you could post the SVG. If you're concerned about copyright issues and such, you can leave out eg. the bus, singer, light and such, leaving only the blue rectangle, the text and the greyish rectangle in the back. But leave the layers and such as they are... just make a stripped copy presenting the same behavior and post that...
Then surely some of the Inkscape gurus here present will sort it out in a jiffy

Also, there are always (at least?) two places to set transparency: in the layer dialog, and also on the objects fill (and stroke), it has happened to me to get confused by that. Also, are all layer blend modes set to normal (in the layers dialog), could have something to do with that?

Actually, I just got it sorted out! I didn't know about the layers dialogue box before and when I went to open it the layer that the text and square were on were at 100% with a normal blend mode. I added another layer just to test and it suddenly read that the square was set at 58% opacity in the fill and stroke section. I set it to 100% and now everything's back to normal. Thank you for your suggestions!

You're welcome. Great that you got it sorted out.