Are there known bans on the Machine Readable section of some UK Passports?

Over the last couple of years, with the introduction of the electronic passport gates at Heathrow (LHR) - I've found I've had a 0% success rate of getting through them, with the system always flagging me to see a human - who manually checks my passport and lets me through.
Until now, I've assumed this was just bad luck (or personal incompetence at using these scanners).
However, when recently applying for an ESTA to visit the USA - I tried to use their "Upload passport" functionality, that asks specifically for the Machine Readable section at the bottom of a passport. Every time I tried, it was refused with an error about not being readable. (Just to be clear, my passport itself is definitely not blocked - as inputting the information manually was approved without issues, and the ESTA was approved).
It's got me wondering, are there any known bans on certain British Passports (e.g. ban lists, or codes embedded into the Machine Readable section) that forces the holder to always see a human for entry, or otherwise blocks use of the Machine Readable section? Or is this just a case of repeat bad luck/user incompetence?
Note, this is in reference to the Machine Readable section, of written characters, on the main picture-page. Not an embedded electronic/biometric chip.
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How do I know if I have a machine readable passport?
If you want to check whether your passport is machine-readable, you can easily check yourself by looking at the identity page. Usually, the data will appear at the bottom of the page. If you see lines of text which include letters, numbers, and symbols, then your passport is machine-readable.What is machine readable zone in passport?
MRZ or Machine Readable Zone is a particular area in an identity document (passport specifically) that encloses the document holder's personal data. Nowadays, almost every country's official identity or travel documents have MRZ, containing confidential information encoded.What does Type P mean on a British passport?
P-type passports are \u201cPersonal passports.\u201d These are the same blue passports that are issued to ordinary citizens for personal purposes like business trips, vacations, or traveling and studying abroad.Is my passport damaged UK?
Your passport could be considered to be damaged or showing signs of wear and tear if one or more of the following criteria are met: your personal details are difficult or impossible to read. the laminate portion on your name page has lifted so that it has the potential for a substitute photo to be inserted.How forged passports are caught in UAE
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