Only a small subset of songs are shuffled on Chromecast, close to the first song played

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Plan

Premium

Country

UK 

Device

Chromecast, cast from Galaxy S8.

My Question or Issue

This has been going on for at least a year and still isn't fixed, the old threads are now closed because they are out of date, but it's still ongoing. If you click shuffle play, or pick manually and toggle shuffle, and then play through a Chromecast the first song is random, but then the subsequent songs are all guaranteed to be close neighbours in the song list. This results in only the same 4/5 albums being shuffled in a song collection of over 9,000. 

Steps to reproduce:

Play song at top of the song list, cast to Chromecast and toggle shuffle. Only songs in the top 50 or so of the song list will ever be selected for the shuffle and played via the Chromecast. 

Expected behaviour:

Entire song collection has an equal chance of being selected for shuffle play.