App+ Skipping 1 month when clicking next month during August jumps to October

Hi, im having some issues witht he App + plugin.
Currently it is set so that you cannot book more than 32 days in advance. there is also a holliday period actice between 24th August to 8th Sept. However as we are currentyly 22 August then Appointments between the 8th and 22nd should be available to book.

Currently when the user selects next month i.e. for September it jumps from August to October missing out September?

Could someone please take a look. - https://monosnap.com/file/dEj0aO1aGyIU5z0toLASDk6Y3ckE32

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Thanks
Tom