Same problem here.

This is caused by these 4 occurrences of cache_expiration_time
https://github.com/simplepie/simplepie/blob/master/src/SimplePie.php#L1676
https://github.com/simplepie/simplepie/blob/master/src/SimplePie.php#L1769
https://github.com/simplepie/simplepie/blob/master/src/SimplePie.php#L1920

cache_expiration_time => should be => __cache_expiration_time

Or at least the array index should be consistent everywhere...

The default file cache is deprecated an will be removed in the next major release. Instead you should use a PSR-16 cache implementation like Symfony Cache or every other implementation.

$simplepie = new \SimplePie\SimplePie();
$simplepie->set_cache(
    new \Symfony\Component\Cache\Psr16Cache(
        new \Symfony\Component\Cache\Adapter\FilesystemAdapter()
    ),
);

Then, a simple example on how to then set the cache type (i.e. file), location and duration would be nice.
The current documentation only mentions a deprecated example and does not say anything about PSR-16 ...

At least it's clear that the PSR-16 changes in #752 broke the legacy cache.
I think reverting 3ba7c91 will fix this bug
Would you consider this, please?

Then, a simple example on how to then set the cache type (i.e. file), location and duration would be nice. The current documentation only mentions a deprecated example and does not say anything about PSR-16 ...

The code example is from #777. Setting cache type and location is part of the PSR-16 implementation. The cache duration is still configured using $simplepie->set_cache_duration($seconds);.

I still don't see an example that one can easily copy/past and just fill in 2 or 3 parameters.
Not everyone can read the whole PSR-16 spec to write a few lines of code...

I still don't see an example that one can easily copy/past and just fill in 2 or 3 parameters.

Please take a look again at my comment above. It already shows you a working example using Symfony Cache using the FilesystemAdapter. But you are free to choose another adapter or even every other implementation.

Not everyone can read the whole PSR-16 spec to write a few lines of code...

You don't have to read the PSR-16 spec. You have to look at the more than 100 implementations (and the PSR-16 spec allows you to try and use them all). Choose the one that works best for you. No one knows your project and use case better than you do.

The example above does not show how to define the (custom) cache file location.
Which PSR-16 is really not so important, so any will do, that is why people needs a simple example

The example above does not show how to define the (custom) cache file location. Which PSR-16 is really not so important, so any will do, that is why people needs a simple example

The file location in the FilesytemAdapter is not required, it uses sys_get_temp_dir() by default. If needed please read the docs for more customization.

I would like to avoid more complex examples for a specific library. Mentioning the Symfony cache implementation alone is already very opinionated. Using the filesystem adapter as cache type is also opinionated. If you would like to have a more customized example for this library in the docs you are welcome to open a PR.

I've found the reason for this issue and opened #846.

@bart-v Could you please confirm that this PR will fix your issue?

Looks good, please go ahead