Does a WhatsApp Chat Messaging subscription created through an Automated Import Definition expire or need to be refreshed periodically?

Hello experts! 

I have a question about WhatsApp Chat Messaging subscribers in Salesforce Marketing Cloud. 

We have integrated WhatsApp in SFMC to send promotional WhatsApp messages from Journey Builder. We are also using Data Cloud, where we created a segment with opted-in clients and activated/exposed it as a Data Extension in Marketing Cloud. 

To make these contacts available for WhatsApp sends, we created an Automated Import Definition to subscribe the opted-in contacts to our WhatsApp Chat Messaging channel, following this article: https://help.salesforce.com/s/articleView?id=000396825&type=1

During testing, we noticed that a contact subscribed through the Automated Import Definition can receive WhatsApp messages successfully, but after some time it seems that the contact may need to be imported/subscribed again to receive later WhatsApp messages. 

My questions are:

1. Does a WhatsApp Chat Messaging subscription created through an Automated Import Definition expire or need to be refreshed periodically?
2. Is it enough to import/subscribe each opted-in contact only once?
3. Or is it recommended to run the import automation regularly, for example before each campaign or every few hours?

Thank you!