Uncovering a problem like this typically involves going through a series of steps. The first thing I suggest is to do a safe mode restart. You restart your computer while holding down the shift key at startup. Then I would run the disk utility app. It is not complicated. It's located in the Utilities sub folder in the Applications folder. In its window, under your Apple HDD icon, click on Container Disk 1 to select it. Then go up to the top and select First Aid. It may take a couple of minutes to run. Expand its window so you can see what it's doing. If there are errors, you will see them reported. At the end It should say it's ok. If not, or if you see errors reported, then rerun the app several times until you (hopefully) get an ok result. Then you can restart and see what happens. Sometimes, merely restarting solves a multitude of problems.
If the problems are still there, I would download and run the free EtreCheck app. Be sure to allow full access. It provides a report of your system which someone here can review and hopefully diagnose the problem. Then you can respond here and post the report below at the paper clip (I think).
If you have any antivirus apps installed - remove them. They are not needed in a Mac and they WILL cause any number of problems. They should be fully uninstalled using the vendor's uninstaller, found on their web site.
If the problem still persists, there are additional steps that can be recommended. I hope this helps. Good luck.
