Problems with (I think) the language server and maven cross-project dependencies

This is possibly a PEBCAK or user-ignorance issue.

I work with several Maven projects.
I have project A and project B open in separate VSCOde workspaces. Project B has multiple sub-projects

A subproject of Project B builds a JAR that is a maven dependency in project A.

Project B is quite large. Project A is small (but all are spring boot so there's quite a lot of cruft around).

If in project B I make some change (say, add a method to a class) and "mvn install", then the VSCode doesn't pick up the change in project A. The new method isn't visible.

Java: refresh, Java: force compilation, java: update project configuration don't fix this.
Java: clean the language server workspace sometimes fixes it, but not always. And takes an age so I don't want to be doing this.

The dependencies are all correct as far as Maven is concerned, as a command-line "mvn install" (for example) of Project A succeeds, including the code that calls the new method

Existing the VSCode for Project A and restarting does seem to work, so it looks like some sort of refresh/caching issue

How am I supposed to set things up for this case? (one maven project depending on the artefact of another)?

I've tried adding Project B as a folder to the workspace of Project A - but the LSP seems to have issues with that (I previously reported a non-reproducable bug were @Test run/debug no longer appeared, and when I tried it as a work around for this, I lost the semantic highlighting etc, (I think - the import statements weren't green but white, as they are while the LSP workspace is loading when first opening the workspace).

If I can provide more info/logs etc, please let me know what is needed.

Environment

• Operating System: Windows 10
• JDK version: VSCode says current version is JDK11
• Visual Studio Code version: 1.47
• Java extension version: MS Java 0.9.1, Redhat 0.65.0

Steps To Reproduce

Please see description above, I don't have a small test case. Sorry

[Please attach a sample project reproducing the error]
Proprietary code. I can't.
Please attach logs

Current Result

Expected Result

Additional Informations

Es werden keine Quelldatei, kein Test und keine kleine Reproduktion bereitgestellt. Beginne damit, das Zwei-Workspace-Maven-Szenario des Issues unter Windows mit den aufgeführten Java- und Extension-Versionen nachzustellen, und aktiviere anschließend die language-server logs mithilfe des verlinkten Troubleshooting-Leitfadens. Als abgeschlossen gilt die Aufgabe, wenn Änderungen, die aus Project B installiert wurden, in Project A sichtbar werden, ohne VS Code neu zu starten oder den Workspace des Language Servers zu bereinigen.