My downloaded music keeps deleting and redownloading itself using lots of mobile data and battery

I use an iPhone 6s and I have iOS 14.4.2. I have adequate storage remaining on the phone.

I was first alerted to this by my carrier that started to contact me saying I was approaching my data limits. I use about 5GB of a 20GB allowance in a usual month and my usage patterns have not changed so this was a bit of a shock.

Resetting my usage statistics it soon became clear it was the default iOS music app that was consuming vast quantities of data. I do not have any music streaming subscriptions.

When I prevented the music app from being able to use mobile data it then told me nearly all my songs paid for through iTunes were unavailable as they were not downloaded to the phone. Not entire albums, just most of the songs, seemingly chosen at random.

When I was next connected to WiFi I redownloaded all my paid for music and checked it by looking under the ‘downloads’ tab in the music app. Automatic downloads was left on.

The next morning I was in public and listening to one of my paid for albums when it cut out unexpectedly. When I checked the music app the track I had just been listening to was now greyed out saying it was not on the phone and would have to be downloaded. It had seemingly deleted itself as I was listening to it. When I checked my other music the same thing had happened as before, the majority of the tracks were greyed out and had erased themselves, apparently at random and some of the tracks that remained were different to the ones that had stayed behind last time.

When I returned home the phone connected to the WiFi and promptly redownloaded the missing tracks. I noticed this because the phone got very hot and lost a large chunk of battery very rapidly. I checked the music app and could see the tracks downloading again.

This is cycle has now been repeating for over a week with a random selection of songs erasing themselves at seemingly irregular times over and over again. Each time it does it it redownloads them when in range of WiFi (songs will still erase themselves when I am at home and connected to WiFi) but I will only notice this happening as the phone suddenly gets very hot and my battery life plummets.

I have now turned off automatic downloads for music as the cycle can repeat several times in a day and it means the phone needs to be charged up all the time. This also means I can’t access the music I have paid for without risking using all my data or costing a large section of battery life.

Please help with this issue.