supervisor: Can't remove addon: 400 Client Error: Bad Request ("invalid reference format")

Environment

Home Assistant 0.98.3 on Raspberry Pi 3B+ (Official Hass.io Image)

Problem

When removing a custom add-on, the following error is logged and the addon is not removed:

400 Client Error: Bad Request (“invalid reference format”)

The container CAN be successfully deleted via Portainer, but this does not remove the addon reference in the Addon UI.

This MAY not necessarily be a bug with Hass.io, but I don’t know what I could be doing differently to get this addon to work.

Addon Repo: https://github.com/qJake/hassio-addon-repository

System Logs

19-09-08 15:03:03 INFO (SyncWorker_18) [hassio.docker.addon] Start Docker add-on qjake/hacc-hassio-armv7 with version 
19-09-08 15:32:10 INFO (SyncWorker_5) [hassio.docker.interface] Stop addon_ac23ff49_hacc application
19-09-08 15:32:12 INFO (SyncWorker_5) [hassio.docker.interface] Clean addon_ac23ff49_hacc application
19-09-08 15:32:12 INFO (SyncWorker_5) [hassio.docker.interface] Remove image qjake/hacc-hassio-armv7 with latest and 
19-09-08 15:32:12 WARNING (SyncWorker_5) [hassio.docker.interface] Can't remove image qjake/hacc-hassio-armv7: 400 Client Error: Bad Request ("invalid reference format")

Addon Dockerfile

# ASP.NET Core 3.x Runtime
FROM mcr.microsoft.com/dotnet/core/aspnet:3.0-buster-slim-arm32v7 AS dotnet

ARG TAG

ENV HACC_VERSION $TAG
ENV ASPNETCORE_URLS http://*:8095
ENV ASPNETCORE_ENVIRONMENT Production
ENV LANG C.UTF-8

EXPOSE 8095

WORKDIR /

RUN apt-get update -yq && apt-get install -yq wget

RUN mkdir /app \
    && cd /app \
    && wget -qO app.tar.gz https://github.com/qJake/HADotNet.CommandCenter/releases/download/v$TAG/HADotNet.CommandCenter-armhf.tar.gz \
    && tar xzf app.tar.gz \
    && rm -rf app.tar.gz

WORKDIR /app

CMD ["dotnet", "HADotNet.CommandCenter.dll"]

# Build arguments
ARG BUILD_DATE
ARG BUILD_REF
ARG BUILD_VERSION

# Labels
LABEL \
    io.hass.name="HACC" \
    io.hass.description="Wall-mountable tablet interface for Home Assistant." \
    io.hass.arch="armv7|armhf|i386|amd64" \
    io.hass.type="addon" \
    io.hass.version=${BUILD_VERSION} \
    maintainer="qJake <https://github.com/qJake/>" \
    org.label-schema.description="Wall-mountable tablet interface for Home Assistant." \
    org.label-schema.build-date=${BUILD_DATE} \
    org.label-schema.name="HACC" \
    org.label-schema.schema-version="$TAG" \
    org.label-schema.url="https://github.com/qJake/HADotNet.CommandCenter/" \
    org.label-schema.usage="https://github.com/qJake/HADotNet.CommandCenter/README.md" \
    org.label-schema.vcs-ref=${BUILD_REF} \
    org.label-schema.vcs-url="https://github.com/qJake/HADotNet.CommandCenter/" \
    org.label-schema.vendor="qJake"