The problem is probably the same as in this question, but the solution offered there has become inapplicable in the last 8 years.
I have an Eclipse RCP project which is in the process of being transformed to use Tycho (version 2.3.0) instead. The project can be run with Eclipse 2019-06 and the custom target platform built for this project.
Then I have set up Tycho with the same target platform (a separate Maven module referencing the same *.target file used by Eclipse).
But then when I run Maven (version 3.6.3) with the usual "clean install" goals, I get this error message:
[ERROR] Failed to execute goal org.eclipse.tycho:tycho-compiler-plugin:2.3.0:compile (default-compile) on project my.project.module: Compilation failure: Compilation failure:
[ERROR] C:\path\to\a\source\file\in\a\module.java:
[ERROR] /*
[ERROR] ^
[ERROR] The type org.eclipse.swt.widgets.Event cannot be resolved. It is indirectly referenced from required .class files
The target platform specifies the same environment (win32.win32.x86_64) for both Eclipse and Tycho, and both SWT .jar files (org.eclipse.swt_3.111.0.v20190605-1801.jar and org.eclipse.swt.win32.win32.x86_64_3.111.0.v20190605-1801.jar) are in one of the directories making up the target platform.