C2 failed due to "No cached parameters found"

[WBQ1995]

Describe the bug
lotus-worker failed to do C2 because of
"No cached parameters found for stacked-proof-of-replication-merkletree-poseidon_hasher-8-8-0-sha256_hasher-82a357d2f2ca81dc61bb45f4a762807aedee1b0a53fd6c4e77b46a01bfef7820".
However, there is no problem with PC2.

Screenshots
If applicable, add screenshots to help explain your problem.

Version :
lotus version 0.5.6+git.606a58bc

Additional context

2020-09-01T19:34:07.115 INFO filcrypto::proofs::api > seal_commit_phase2: start
2020-09-01T19:34:07.197 INFO filecoin_proofs::api::seal > seal_commit_phase2:start
2020-09-01T19:34:07.197 INFO filecoin_proofs::caches > trying parameters memory cache for: STACKED[34359738368]
2020-09-01T19:34:07.197 INFO filecoin_proofs::caches > no params in memory cache for STACKED[34359738368]
2020-09-01T19:34:07.198 INFO storage_proofs_core::parameter_cache > parameter set identifier for cache: layered_drgporep::PublicParams{ graph: stacked_graph::StackedGraph{expansion_degree: 8 base_graph: drgraph::BucketGraph{size: 1073741824; degree: 6; hasher: poseidon_hasher} }, challenges: LayerChallenges { layers: 11, max_count: 18 }, tree: merkletree-poseidon_hasher-8-8-0 }
2020-09-01T19:34:07.198 INFO storage_proofs_core::parameter_cache > ensuring that all ancestor directories for: "/home/nbfs/nfs_share/filecoin-proof-parameters/v28-stacked-proof-of-replication-merkletree-poseidon_hasher-8-8-0-sha256_hasher-82a357d2f2ca81dc61bb45f4a762807aedee1b0a53fd6c4e77b46a01bfef7820.params" exist
2020-09-01T19:34:07.198 INFO storage_proofs_core::parameter_cache > checking cache_path: "/home/nbfs/nfs_share/filecoin-proof-parameters/v28-stacked-proof-of-replication-merkletree-poseidon_hasher-8-8-0-sha256_hasher-82a357d2f2ca81dc61bb45f4a762807aedee1b0a53fd6c4e77b46a01bfef7820.params" for parameters
2020-09-01T19:34:07.201 INFO filcrypto::proofs::api > seal_commit_phase2: finish
2020-09-01T19:34:07.201Z        ^[[33mWARN^[[0m rpc     [email protected]/handler.go:241  error in RPC call to 'Filecoin.SealCommit2': No cached parameters found for stacked-proof-of-replication-merkletree-poseidon_hasher-8-8-0-sha256_hasher-82a357d2f2ca81dc61bb45f4a762807aedee1b0a53fd6c4e77b46a01bfef7820
github.com/filecoin-project/filecoin-ffi.SealCommitPhase2
        /home/nbfs/code/lotus/extern/filecoin-ffi/proofs.go:401
github.com/filecoin-project/lotus/extern/sector-storage/ffiwrapper.(*Sealer).SealCommit2
        /home/nbfs/code/lotus/extern/sector-storage/ffiwrapper/sealer_cgo.go:515
github.com/filecoin-project/lotus/extern/sector-storage.(*LocalWorker).SealCommit2
        /home/nbfs/code/lotus/extern/sector-storage/localworker.go:169
reflect.Value.call
        /usr/local/go/src/reflect/value.go:460
reflect.Value.Call
        /usr/local/go/src/reflect/value.go:321
github.com/filecoin-project/go-jsonrpc/auth.PermissionedProxy.func1
        /home/nbfs/go/pkg/mod/github.com/filecoin-project/[email protected]/auth/auth.go:62
reflect.callReflect
        /usr/local/go/src/reflect/value.go:549
reflect.makeFuncStub
        /usr/local/go/src/reflect/asm_amd64.s:20
github.com/filecoin-project/lotus/api/apistruct.(*WorkerStruct).SealCommit2
        /home/nbfs/code/lotus/api/apistruct/struct.go:1207
reflect.Value.call
        /usr/local/go/src/reflect/value.go:460
reflect.Value.Call
        /usr/local/go/src/reflect/value.go:321
github.com/filecoin-project/go-jsonrpc.doCall
        /home/nbfs/go/pkg/mod/github.com/filecoin-project/[email protected]/handler.go:130
github.com/filecoin-project/go-jsonrpc.(*RPCServer).handle
        /home/nbfs/go/pkg/mod/github.com/filecoin-project/[email protected]/handler.go:221
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1373

[yihaiy]

Only C2 needs proving-params. You can try to check whether the proof document exists and the version is correct.