Controls disappearing from VBA UserForm in PowerPoint 2016 but OK on 2013/2010

I have a VBA project with several userforms and modules that's evolved over many years. As of today, PowerPoint 2016 on Windows fails to load the pptm project without error and I've tracked it down to one userform in which all of its ~20 controls except one (a MultiPage control) have disappeared and hence the numerous corresponding control events code, which is still present, is complaining.

When I open the project in PowerPoint 2013 or 2010 the userform appears correctly and the project compiles. I have exported the userform from 2010, deleted it from the project in 2016 and re-imported it into the project in 2016. The userform still appears to be empty apart from the one MultiPage control and the project doesn't compile.

This userform isn't the only one using a MultiPage control so I don't think that's the issue. If I remove the userform from the project and the associated .Show method elsewhere, the project compiles normally.

What is going on?!

PowerPoint 2016 PC version 1806 build 10205.20009
LVL 14
Jamie GarrochPowerPoint Consultant & DeveloperAsked:
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Jamie GarrochPowerPoint Consultant & DeveloperAuthor Commented:
Traced the source of the issue to a Shockwave Flash control in the userform. Weird that it makes every other control disappear. When I delete juts that one control on Office 2013, all other controls reappear on 2016. Was there a security update that prevents Office 2016 from using Shockwave Flash control objects now?
Jamie GarrochPowerPoint Consultant & DeveloperAuthor Commented:
I found the following article from Microsoft explaining that Flash, Shockwave and Silverlight controls will be blocked for all 365 users from June 2018. Perhaps it's happened earlier for insider users.

What remains odd about this is that the disabling of these controls can affect all other legitimate controls on a userform..

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Jamie GarrochPowerPoint Consultant & DeveloperAuthor Commented:
Answer found on Microsoft Technet although their implementation of disabling another Office feature  leaves a lot to be desired!
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