I had the same issue. In PreForm there are two buttons, auto update and manual update. You can try the manual update button. If it doesn’t help reach out to Formlabs support…
Hey there, I had the same issue but after contacting support they sent me over two firmware (2.14 and 2.15.4) files in an email. Basicly the new 2.15.4 firmware is unable to be decrypted by the current firmware thus you must do a “progressive” update. First connect to your printer through PreForm and access the update menu, now instead of automatic update select manual update and select firmware file 2.14, then repeat these steps for 2.15.4 and you should be on firmware version 2.15.4
Firmware Links:
2.14 https://s3.amazonaws.com/bessemer-releases/release/form2-rc-1.14.21-154.formware
2.15.4 https://s3.amazonaws.com/bessemer-releases/release/form2-rc-1.15.4-160.formware