Mobile data speed is capped at 64 kB/s

I recently upgraded my phone to android 13 and after the upgrade the mobile connection speed is very slow. On average it doesn't exceed 64 kilobytes per second. Some information about the phone that most likely don't matter: * It's a Xiaomi Redmi 4X * I'm using [Voltage OS 2.8](https://xdaforums.com/t/closed-rom-official-13-voltageos-santoni-eol.4535639/) which builds on Android 13 * Previously I used [Havoc OS 3](https://xdaforums.com/t/rom-official-ten-havoc-os-3-x-santoni-stable.4045593/) on Android 10, but this is too old now. Mobile data speed worked fine. Yes, I still got mobile data volume. And if not I would be capped to 56 kilobits per second. Yes I tested it over multiple days. What could cause this problem? Is there a secret setting for capping mobile speed that might be set? How could I debug this problem? Did I forget any important information? #### Edit on 2024-09-30 I flashed other custom ROMs, I flashed all official stock ROMs, I flashed new firmware, I flashed old firmware, I flashed every available official firmware, nothing changed anything. Even with every official stock ROM, the download speed is capped to 64 kB/s. Then I flashed Lineage 21 and gave up. Some time later the mobile data stopped completely. I had to permit apps to ignore the data saver. The data saver is disabled and always was disabled but permitting apps to ignore a disabled data saver did the trick. I got mobile data again and for about 50% of the time it goes over 64 kB/s. Sometimes it's throttled again for some hours, then it works fine for some hours. This whole behavior is just strange and I'm giving up now. #### Edit on 2024-10-30 The mobile data did not go over 64kB/s again. I bought a new phone, the mobile data is still capped to 64kB/s. I bought a new SIM card, the mobile data is still capped to 64kB/s. If I insert a friends SIM card, it works fine, if I insert my SIM card into other phones, it works fine. May this be a curse? What ingredients do I need to get rid of this? Holy water, sulfur, a crucifix?