Occasionally, a new firmware breaks features. For example, some GM220-S updates remove the ability to change DNS servers or disable TR-069 (remote ISP management). If you want to downgrade:
If your device has "GM220-S" printed on a sticker, it is almost certainly a white-label GPON ONT (often branded with your ISP's logo). Common rebrands include: Firmware Gm220-s
Do not download firmware from random forums. Instead: Occasionally, a new firmware breaks features
Developers constantly optimize code. A firmware update can improve the throughput speed of the GM220-S, reduce latency, or fix bugs that caused the device to freeze under heavy load. Do not download firmware from random forums