It looks like your season pass is connected to your Steam Account , at least based on this web site
https://wastedondestiny.com/1_4611686018431083070,3_4611686018496130092
you should be able to check this out by looking at the licenses on Steam
English
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Licence is there, I definitely 'should' own it So why don't I?
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Its not lost it is hiding in the Steam account that is now dormant and hidden by your cross-save. if you unlink the cross save, warning there is a 90 day waiting period if you unlink the cross save before you can redo the cross save. DO NOT turn off cross save. As you will need to wait 90 days before you can reactivate.