I just rescued two AX92Us with the same problem. My method was:
1. I ordered the xGecu T48. Plus the TSOP 48 socket (30+ bucks for only a d@ng socket!)
2. Ordered 10pc of flash chips, the same as the original (Macronix, labeled as:MXIC MX30LF2G189C)
3. Desoldered the original Macronix MX30LF2G189C from the AX92U (use lots of Amtech flux!)
4. Readed out and saved the flash. In the xGPro, under the Device>Check NAND blocks, there is the tool to check for physical errors.
5. Flash chips are arrived, after checking them with the above mentioned tool, i noticed thet half of them are were garbage, with 1...4...25 bad blocks... And i pulled them out from the factory plastic tray...
6. I flashed a new and 0 bad block flash chip with the orriginal flash dump.
7. Soldered it back, without hot air, only applying heat to the legs with the solder iron, to protect the flash chip (used even more Amtech flux, than on the desoldering. It really helps to get rid of the bridgings!)
8. Turned it on, as i expected, it had error messages on the UART (original flash was saved from the point where the rescue failed due to the bad, unwritable flash chip itself)
9. Started in rescue mode and applied the latest FW. Succeded.
10. Turned on, big smile on my face since. Repeated it on a second 92U.