failed to deserialize factor graph!! unsupported version

[xhgxh]

Describe the bug
When downloading mmm.tar.gz, extracting it, and running the merge example, the map fails to load.

2026-02-26 16:44:30.144] [viewer] [info] enable_optimization=true
[2026-02-26 16:44:30.145] [global] [info] Load submaps (session_id=0)
[2026-02-26 16:44:30.256] [global] [info] deserializing factor graph
[2026-02-26 16:44:30.257] [global] [error] failed to deserialize factor graph!!
[2026-02-26 16:44:30.257] [global] [error] unsupported version
[2026-02-26 16:44:30.257] [global] [info] deserializing values
[2026-02-26 16:44:30.257] [global] [error] failed to deserialize values!!
[2026-02-26 16:44:30.257] [global] [error] unsupported version
[2026-02-26 16:44:30.257] [global] [info] creating matching cost factors
[2026-02-26 16:44:30.257] [global] [info] optimize
[2026-02-26 16:44:30.257] [global] [error] an exception was caught during global map optimization!!
[2026-02-26 16:44:30.257] [global] [error] Attempting to at the key "x1", which does not exist in the Values.
[2026-02-26 16:44:30.257] [viewer] [info] --- smoother_updated ---
count new lin elim gpu_e gpu_l delta time_msec
0 0 0 0 0 0 0 0
terminate called after throwing an instance of 'std::out_of_range'
what(): Requested variable 'x0' is not in this VectorValues.