Web3Signer is an open-source signing service capable of signing on multiple platforms (Ethereum1 and 2, Filecoin) using private keys stored in an external vault, or encrypted on a disk.
Some of the issues seem to be caused by vertx worker pools being full. Added an option to web3signer to allow the worker pool size to be configurable https://github.com/Consensys/web3signer/pull/920
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