Outlook Web Addin: Ribbon toolbar icon not visible on Mac

Question

This is Mac-only issue(icon shows in Outlook 2013 and Outlook 2016 for Windows, all the web browsers and even on Macbook pro).

The testing environment I used was

Outlook for Mac 2016 (version 16.16.4 (181110))

Mac OS version 10.13.4

I was given this feedback when I submitted my Outlook web add-in to the store for testing.

Your add-in is not working in the Outlook Client on Mac in read mode on a message. Your add-in icon appears to not load correctly

I believe I have follow the guidelines when providing the icons and I use Https for reference.

Interestingly I cannot replicate this issue in my Mac book pro but only in a Mac.

Here is the link to the screenshot: https://i.stack.imgur.com/F1Odq.png

Here is my manifest icon section:

<Icon>
    <bt:Image size="16" resid="icon16" />
    <bt:Image size="32" resid="icon32" />
    <bt:Image size="64" resid="icon64" />
    <bt:Image size="80" resid="icon80" />
</Icon>
<bt:Images>
    <bt:Image id="icon16" DefaultValue="https://{resource}.16png"/>
    <bt:Image id="icon32" DefaultValue="https://{resource}.32png"/>
    <bt:Image id="icon64" DefaultValue="https://{resource}.64png"/>
    <bt:Image id="icon80" DefaultValue="https://{resource}.80png"/>
</bt:Images>

What I have done so far:

1. include a 64x64 pixel icon in the manifest (the doc says it is recommended for Mac)
2. make the icon not transparent
3. include all optional sizes of icons (40x40 pixel etc)
4. delete and re-add the add-in
5. re-launch outlook for Mac
6. Change the content of the icon

Answer 1

Found the answer, the 32x32 icon is corrupted, after I replaced it with a good quality one,the icon now shows in Outlook for Mac. Interestingly all other Outlook host have higher tolerance over corrupted image than Outlook for Mac.