frequency subscription

Hello,
I have a singe-product on sale by subscription on my woocommerce.
Several subscription frequencies can be chosen and can be changed at any time by the user.
Everything is OK when the user changes from 2 weeks to 3 weeks, to 4 weeks to 2 weeks on so on for 2,3,4,5,6 weeks… But it does not work when the user changes from any frequencies to 2 months.
In detail the issue is that the user continues to pay according to the former frequency (and not every 2 months). The issue is only when he changes from any frequency to 8 weeks. For example, when the user changes from 2 weeks to 4 weeks, the debit automatically changes from 2 weeks to 4 weeks
Thx

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