Why am I not receiving most WhatsApp texts on my iPhone?

Hi,

Really appreciate help for this:

I can send whatsapp messages, but am receiving only some whatsapp texts back from my contacts. Mostly from groups. 80% of whatsapp texts are not reaching me.

My contacts are seeing single ticks when they send me messages, even when I have their chat open. I have tried rebooting my iPhone, and cleared up more than 10GB space on my device.

I've updated Whatsapp. I've enable Background App Refresh for Whatsapp. I have definitely not been blocked by all my contacts. I've checked that I am not on Focus or Do Not Disturb mode. I have tried sending & receiving texts on data and on Wifi. I have logged off Whatsapp on all devices other than my iPhone, and it hasn't made a difference.

What is causing this?

[Re-Titled by Moderator]