Over the lifetime of a product it may undergo changes to sustain its production. Many of these changes are done for efficiencies, optimization, replacing components that can no longer be sources and are minor and not noticable noticeable to the user, ever. These may include changes to memory components used, microporcessor, AD-DA converters and FPGA.
...
Due to this reason the device built with new components may be intentionally restricted from being loaded with a firmweare firmware version that does not have support for the hardware. In this instance the user will be notified that the device cannot accept the older firmware / software version and inhibit the downgrade.
...
HelixNet - Units built as of 2023@Q1 cannot run older firmware than version HMS4.4 or Arcadia 2.8
Arcadia - Units built in 2023H1 cannot run older firmware than version 2.8
FSE-BASE - Units built in 2023H1 cannot run older firmware than version 2.8
FSII-IPT - Units built as of 2023@H1 cannot run older firmware than version 5.39.67.0
FSE-TCVR - Units built as of 2023@H1 cannot run older firmware than version 4.26.77.0
IRIS - Units built as of 2023@H1 cannot run older firmware than version 6.47.73.0
This list is not compleatecomplete, yet serves as an example of where products are intentionally restricted from downgrades.