solomining error with rpcworkqueue

[cryptozeny]

hi i got an error when solomining. it stops with this error. restart deftd solves issue, but i don't know why it causes...

deft
now working perfectly with libssl versions 1.0.2 and 1.1.0
os
'ubuntu 16.04 LTS 64bitcpuminerofficial deft`

debug.log

2018-06-27 08:00:35 WARNING: request rejected because http work queue depth exceeded, it can be increased with the -rpcworkqueue= setting

cpuminer log

[2018-06-27 16:59:45] json_rpc_call failed, retry after 10 seconds
[2018-06-27 16:59:55] JSON decode failed(1): '[' or '{' expected near 'Work'

any idea?