What breaks after flashing a custom ROM

Many banking, payment and ticketing apps, and some games, check the phone with Google's Play Integrity API. It returns levels, and each app decides which one it demands:

• Basic integrity allows a locked or unlocked bootloader and an uncertified device.
• Device integrity requires a genuine, certified device — on Android 13 and later, hardware-backed proof that the bootloader is locked and the OS is a certified manufacturer image.
• Strong integrity adds a security update within the last year.

A custom ROM can't honestly pass device integrity — it isn't a certified manufacturer image, and its bootloader is usually unlocked too — so an app that requires that level will refuse to run or disable features. Workarounds that spoof the result exist; they're an arms race that can break with any update, and an app that works this month may not next month. Some apps also check for root separately. GrapheneOS, which runs locked, documents how app developers can use hardware attestation to accept it — but that's up to each app.

That's why CustomDroid doesn't say whether banking “works” on a ROM: it depends on the app, the phone and the month. If an app is essential, check recent reports for your bank before you flash (readers' dated reports are on the banking apps page), and keep a fallback such as the bank's website.

Google is explicit here. Its Wallet help page says contactless payments don't work on phones that are rooted, run a custom ROM, have modified factory software or have an unlocked bootloader, and that you must reinstall the original OS to pay. Samsung phones lose Samsung Pay/Wallet permanently once Knox is tripped, even after going back to stock. Other banks' own tap-to-pay apps often rely on the same integrity checks as above.

Streaming services protect video with Widevine DRM. Its highest level, L1, uses the phone's hardware-backed security; the fallback, L3, is software-only. On some phones, unlocking the bootloader or flashing a ROM drops Widevine from L1 to L3, and streaming apps then limit playback to lower resolutions. On some devices L1 returns after relocking on stock firmware; on others it doesn't.

Sony is the clearest case: its unlock page warns that unlocking erases the phone's DRM security keys, and those don't come back. A free DRM information app from the Play Store shows your current Widevine level — worth checking before you unlock if HD streaming matters to you.

Much of a modern phone camera's quality is software: the manufacturer's camera app and its image processing, which are proprietary and stay behind on stock. A custom ROM usually ships a basic open-source camera app, so photos and video — night shots, HDR and stabilisation in particular — can be noticeably worse, and extra lenses or modes may be missing. Some ROMs include a better camera for certain devices, and community camera ports exist for some phones. On some Sony models, the loss of DRM keys also degrades camera processing, according to Sony.

Voice over LTE, Wi-Fi calling (VoWiFi) and 5G depend on carrier-specific configuration that the manufacturer ships and tests for each network. A custom ROM may not carry the right profile for your carrier, and the result can be calls that don't connect, no Wi-Fi calling, or no 5G — even when the same ROM works perfectly on another network.

This matters more every year: where 2G and 3G networks have been switched off, a phone without working VoLTE may not be able to make calls at all. Check reports from people on your carrier, not just your phone model.

Fingerprint sensors rely on vendor drivers that a ROM maintainer has to get working per device. They usually do, but under-display sensors in particular can be slower or less reliable than on stock. Face unlock is often a manufacturer feature that isn't carried over at all.

You stop receiving the manufacturer's updates — Sony says so outright for unlocked Xperias. Updates now come from the ROM: official builds often update over-the-air through a built-in updater, while unofficial ones may need manual flashing (see official vs unofficial builds).

The phone's firmware— modem, bootloader and other vendor parts — may not be updated by the ROM at all. Some ROMs require a specific firmware version before you install; LineageOS's install guides warn that the wrong firmware can cause crashes and broken features. And when the ROM stops supporting your phone, the updates stop too — what end-of-life means.

Adding or switching eSIM profiles needs an eSIM manager on the phone. Some ROMs include one; on others it may only arrive with Google's apps, and on some builds adding an eSIM isn't possible at all. Before wiping a phone that uses an eSIM, find out how your carrier reissues one — you may need a new activation code.

Everything the manufacturer built on top of Android goes: its gallery edits, desktop modes, special gestures, and cloud services. The LineageOS install guides note that backups made with manufacturer tools, such as Samsung's or Motorola's, may not be accessible from a custom ROM — back up in a portable format.