Plugin based on template fails to be recognized as a plugin zip

I've been trying to update and upgrade an older plugin which while upgrading the build process to be based on the GitHub template.

While the built plugin loads and works in various IDEs at 2020.3, it comes up with the following error when trying to load the same plugin into various IDEs at >=2021.1. The error:

The source for the plugin is here -> https://github.com/ServiceStack/ServiceStackIDEA

Asset from GitHub Action build here -> https://github.com/ServiceStack/ServiceStackIDEA/releases/tag/v1.2.0-nightly

The `gradle.properties` for the build is below:

# IntelliJ Platform Artifacts Repositories
# -> https://plugins.jetbrains.com/docs/intellij/intellij-artifacts.html

pluginGroup = ServiceStackIDEA
pluginName = ServiceStack
pluginVersion = 1.2.0-nightly

# See https://plugins.jetbrains.com/docs/intellij/build-number-ranges.html
# for insight into build numbers and IntelliJ Platform versions.
pluginSinceBuild = 192
pluginUntilBuild = 211.*

# Plugin Verifier integration -> https://github.com/JetBrains/gradle-intellij-plugin#plugin-verifier-dsl
# See https://jb.gg/intellij-platform-builds-list for available build versions.
pluginVerifierIdeVersions = WS-2019.3.4, 2019.3.4, 2021.1.1

platformType = IC
platformVersion = 2019.3.4
platformDownloadSources = true

# Plugin Dependencies -> https://plugins.jetbrains.com/docs/intellij/plugin-dependencies.html
# Example: platformPlugins = com.intellij.java, com.jetbrains.php:203.4449.22
platformPlugins = maven, java, PythonCore:193.6911.18

# Opt-out flag for bundling Kotlin standard library.
# See https://plugins.jetbrains.com/docs/intellij/kotlin.html#kotlin-standard-library for details.
kotlin.stdlib.default.dependency = false

The `pluginUntilBuild = 211.*` version I believe is inclusive, but could this please be confirmed? Hoping this is a simple fix, any suggestion would be appreciated. Thanks!