I may have an answer for this.
I’ve done some unintentional investigating due to the new Team quests.
- I turned ON the setting ‘Vibrate When Invited To Defend’ - suddenly i wasn’t getting any banners (i didn’t realise this yet)
- I got fed up of waiting for defend banners so decided to attack myself with an alt - No Banner
- I realised that my phone was still vibrating from time to time as if i was recieving an invite. I thought it was weird so decided to turn the setting OFF (vibrate when invited to defend) - The banners returned
I hope this works for some other people on this thread - Please try it and let us know if it works for you.
edit: added tag @Blaze