Ironically, ad / cookie blocking plug-ins can interfere with the frequency capping itself so if you try disabling any ad blockers, the trailers should work as expected.
If this does not fix it, have you selected the option "Do Not Personalize Ads from Amazon for this Internet Browser" on https://www.amazon.com/adprefs ? By selecting this option, Amazon would not apply frequency capping on your requests, and this would explain the behaviour since you are essentially opting out of us storing any information, including whether or not you have already seen the ad.
If none of the above works, please let us know the system and browser which you are using plus also the country from which you are accessing IMDb.
No, I haven't selected that Amazon option, in fact I didn't even know it existed.
I'm not too bothered about the ads, most of them have a 'skip ad' option anyway. It's the Orient Express trailer that's so annoying; it comes up in place of any trailer I click on, and won't go away, so I can never get to see the trailer I want to. This only started happening recently.
I'm using Internet Explorer and Google, from the UK.
Sorry, the advice on the IMDb post takes me rather beyond my (very limited) area of comprehension. I have no idea what a 'private/incognito tab' is.
The following - largely at random - trailer links have all given me the Orient Express trailer: Lost in Paris, Manifesto, Killing of a Sacred Deer, The Lobster, Darkest Hour....