@imagejan, could you please have a look whether you can reproduce this bug? @TobiasKletter said to me in a private communication that this not specific to the Spindle Morphometry plugin, but a general issue (I am mentioning this because I was worried that something on my EMBL-CBA screws something up, but apparently this is not the case).
TL;DR: this issue is fixed since last Friday, please update your Fiji installation and report back if you continue to see issues.
A bit more detail:
The issue was caused by scijava-common-2.80.1.jar which was recently uploaded by @ctrueden to fix an issue with IJ2 Options plugins, but which caused ModuleBatchProcessor and other plugins that extend DynamicCommand to fail due to a duplicate Parameter declaration.
It was brought to my attention by mikeumo in this GitHub issue:
Usually, this kind of issues should be caught by unit tests, but in this case, uploading a version of scijava-common (2.80.1) which was newer than (and incompatible with) the version declared in pom-scijava (2.77.0) led to a version skew with problems that my tests couldn’t catch.
I had to fix it by manually pinning the scijava-common version to 2.80.1 until a new pom-scijava is released:
As far as I can tell, @ctrueden is working on a more automated management of the components uploaded to the update sites, including a melting-pot script that tests inter-operability of versions of all the components in the SciJava software stack, so hopefully this kind of issues will be detected much earlier, before it affects users in this way.