user6691: Using blockfrost I have pulled a list of addresses of owners of a specific fungible token.
Some of the addresses are significantly smaller than the others (about  2/3 the length).
When querying blockfrost for stake keys (or pool.pm) with those addresses i get an error 504 after a long timeout, while all the others work smoothly.
An example of the syntax and function used with python is the following api.address(addr_str)
Here is the address causing me trouble addr1w999n67e86jn6xal07pzxtrmqynspgx0fwmcmpua4wc6yzsxpljz3
How should I handle those, what are they?

user5167: Those are called Enterprise addresses, originally intended for exchanges but everyday users have started to adopt them for various reasons. Unfortunately, I can't speak to why Blockfrost API chokes when it encounters one, but there are other APIs that support these. Try Koios for example.
https://api.koios.rest/#get-/address_assets
EDIT: Ah! Just noticed an important part of your message.. The reason you're getting the timeout error is because enterprise addresses do not have stake addresses as they were never meant to stake (again they are intended for exchanges). That's why this is timing out.

6691: <p>Using blockfrost I have pulled a list of addresses of owners of a specific fungible token.
Some of the addresses are significantly smaller than the others (about  2/3 the length).</p>
<p>When querying blockfrost for stake keys (or pool.pm) with those addresses i get an error 504 after a long timeout, while all the others work smoothly.</p>
<p>An example of the syntax and function used with python is the following <code>api.address(addr_str)</code></p>
<p>Here is the address causing me trouble <code>addr1w999n67e86jn6xal07pzxtrmqynspgx0fwmcmpua4wc6yzsxpljz3</code></p>
<p>How should I handle those, what are they?</p>
 5167: <p>Those are called Enterprise addresses, originally intended for exchanges but everyday users have started to adopt them for various reasons. Unfortunately, I can't speak to why Blockfrost API chokes when it encounters one, but there are other APIs that support these. Try Koios for example.</p>
<p><a href="https://api.koios.rest/#get-/address_assets" rel="nofollow noreferrer">https://api.koios.rest/#get-/address_assets</a></p>
<p>EDIT: Ah! Just noticed an important part of your message.. The reason you're getting the timeout error is because enterprise addresses do not have stake addresses as they were never meant to stake (again they are intended for exchanges). That's why this is timing out.</p>
