Clean build - 70% of the time, it solves the problem every time.
We'd like to understand every problem before solving, but sometimes it's just easier start with a clean slate and see if that works.
So if you're using IntelliJ and maven, here is how to do that.
Make sure you have no suspicious changes in your workspace.
If you want to be really through, you can delete this directory, in order to make maven get all dependencies anew C:\Users\YOUR_USERNAME\.m2\repository I rarely include this step, it's too much extra time, and most problems haven't been in maven dependencies for me.
Open Bash or PowerShell, navigate to your project directory, and type
mvn clean mvn package -pl :YourProjectName -am -DskipTests
It sometimes helps to build with maven instead of IntelliJ, because they don't always follow the exact same build plan.
Clear IntelliJ cache and restart:
ctrl+shift+A "Invalidate caches / restart"
Reimport all maven projects
ctrl+shift+A "Reload all maven projects"