First Party Ads load, flash, then are removed after full page load

[willstocks_tech]

Description of the issue:
When I navigate to a site that I own/run (https://willstocks.co.uk), I see my first-party sidebar ad (and footer) image flash up for about a second upon load, then something kicks in (assume a native ad blocker?) and applies style {display: none !important;} to those elements.

These ads have previously shown without an issue and it appears to be a “UA Style” being applied.

It’s unclear whether there was a change that blocks first party ads natively by default now? If they are, why are they being allowed to load at all, flash and then disappear (bad UX). If they’re not, why is this happening and what can I do to resolve?

Exact URL of the website in question:

Will Stocks

Did the issue present with default Shields settings? (yes/no)

Yes

Does the site function as expected when Shields are turned off?

Yes if I am still supposed to be able to see first party ads

Is there a specific Shields configuration that causes the site to break? If so, tell us that configuration. (yes/no):

N/A

Does the site work as expected when using Chrome?

Yes

Brave version (check About Brave):

Version 1.9.76 Chromium: 81.0.4044.138 (Official Build) (64-bit)

[fanboynz]

First-party items will be blocked in Brave, the adblocker in Brave has been improving. Probably the easier way to resolve it is change the div element name, or avoid ads being hosted on the site?