Eclipse project missing required library that is not a dependency - eclipse

Question

I'm using Eclipse version 2019-03 (4.11.0) and I have a project with a big red exclamation mark to the left of the project name. I am not using any dependency management tool, I am managing my dependencies myself manually. The Problems view is telling me that my project is missing a required library, but that jar file is no longer in my list of dependencies for the project (I replaced it with an upgraded version recently, and the problem has existed since then). In case this was a GUI issue I checked the .classpath file for the project in a text editor and it's not listed there. I've also tried cleaning and re-building the project.
This problem is masking compile error and warning icons over the source files in my project. Is there something obvious I've missed? (before I attempt to recreate the project from scratch).
The error listed under the Problems view is:
Project 'MyProject' is missing required library: '/home/me/eclipse-workspaces/work/MyProject/xyz.jar'
The Location is Build Path and the Type is Build Path Problem.
Here's an edited version with the relevant stuff in my .classpath (the supposed missing jar is NOT listed in this file):
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8"/>
<classpathentry kind="src" path="src"/>
<classpathentry kind="lib" path="/home/me/eclipse-workspaces/work/MyProject/somelib.jar"/>
<classpathentry kind="lib" path="/home/me/eclipse-workspaces/work/MyProject/anotherlib.jar"/>
<classpathentry combineaccessrules="false" kind="src" path="/Enki-Utils"/>
<classpathentry kind="output" path="bin"/>
</classpath>
The only other Eclipse related file in my project root directory is .project:
<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
<name>MyProject</name>
<comment></comment>
<projects>
</projects>
<buildSpec>
<buildCommand>
<name>org.eclipse.jdt.core.javabuilder</name>
<arguments>
</arguments>
</buildCommand>
</buildSpec>
<natures>
<nature>org.eclipse.jdt.core.javanature</nature>
</natures>
</projectDescription>

Answer 1

The solution for me was to close and re-open the project (without restarting Eclipse) which must have flushed out some stale cache. The accepted answer for this question got it for me (with some other possible solutions if that doesn't work).