@Martin Thanks for your patience. The host machine was actually unplugged and moved between my first post and your response. I’ve got it running again now. 
Here are the first 106 lines of the stack trace. An additional 5500+ lines of goroutine traces were also produced. I can post some or all of those if needs be.
fatal error: concurrent map read and map write
goroutine 3632 [running]:
runtime.throw(0xe158a0, 0x21)
/usr/local/go/src/runtime/panic.go:530 +0x90 fp=0xc823d016e0 sp=0xc823d016c8
runtime.mapaccess2_faststr(0xb1f380, 0xc820127860, 0xc8246e4c00, 0x18, 0xc826b81ea0, 0x1)
/usr/local/go/src/runtime/hashmap_fast.go:307 +0x5b fp=0xc823d01740 sp=0xc823d016e0
main.(*OrganizationMonitor).ProcessRequestOffThread(0xc824701d60, 0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0, 0x0, 0x0, 0x0, 0x0, 0x10cad82d0962d12b)
/home/tyk/go/src/github.com/lonelycode/tyk/middleware_organisation_activity.go:136 +0x26d fp=0xc823d01810 sp=0xc823d01740
main.(*OrganizationMonitor).ProcessRequest(0xc824701d60, 0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0, 0x0, 0x0, 0x0, 0x0, 0x5e91810b3d3ef424)
/home/tyk/go/src/github.com/lonelycode/tyk/middleware_organisation_activity.go:37 +0x75 fp=0xc823d01860 sp=0xc823d01810
main.CreateMiddleware.func1.1(0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0)
/home/tyk/go/src/github.com/lonelycode/tyk/middleware.go:44 +0x178 fp=0xc823d01918 sp=0xc823d01860
net/http.HandlerFunc.ServeHTTP(0xc823e79680, 0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0)
/usr/local/go/src/net/http/server.go:1618 +0x3a fp=0xc823d01938 sp=0xc823d01918
main.CreateMiddleware.func1.1(0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0)
/home/tyk/go/src/github.com/lonelycode/tyk/middleware.go:54 +0x26f fp=0xc823d019f0 sp=0xc823d01938
net/http.HandlerFunc.ServeHTTP(0xc823e796c0, 0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0)
/usr/local/go/src/net/http/server.go:1618 +0x3a fp=0xc823d01a10 sp=0xc823d019f0
github.com/gorilla/mux.(*Router).ServeHTTP(0xc82020cc80, 0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0)
/home/tyk/go/src/github.com/gorilla/mux/mux.go:98 +0x29e fp=0xc823d01b28 sp=0xc823d01a10
net/http.(*ServeMux).ServeHTTP(0xc820010cc0, 0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0)
/usr/local/go/src/net/http/server.go:1910 +0x17d fp=0xc823d01b80 sp=0xc823d01b28
net/http.serverHandler.ServeHTTP(0xc825bd2b00, 0x7f6a6c86ecf8, 0xc826b92b60, 0xc826b81ea0)
/usr/local/go/src/net/http/server.go:2081 +0x19e fp=0xc823d01be0 sp=0xc823d01b80
net/http.(*conn).serve(0xc826b63900)
/usr/local/go/src/net/http/server.go:1472 +0xf2e fp=0xc823d01fa8 sp=0xc823d01be0
runtime.goexit()
/usr/local/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc823d01fb0 sp=0xc823d01fa8
created by net/http.(*Server).Serve
/usr/local/go/src/net/http/server.go:2137 +0x44e
goroutine 1 [chan receive, 10 minutes]:
github.com/rcrowley/goagain.Wait(0x7f6a6c869858, 0xc820022240, 0x7f6a6c869858, 0x0, 0x0)
/home/tyk/go/src/github.com/rcrowley/goagain/goagain.go:207 +0x488
main.main()
/home/tyk/go/src/github.com/lonelycode/tyk/main.go:1302 +0x2414
goroutine 17 [syscall, 10 minutes, locked to thread]:
runtime.goexit()
/usr/local/go/src/runtime/asm_amd64.s:1998 +0x1
goroutine 5 [chan receive, 10 minutes]:
github.com/getsentry/raven-go.(*Client).worker(0xc8200ff8c0)
/home/tyk/go/src/github.com/getsentry/raven-go/client.go:415 +0x60
created by github.com/getsentry/raven-go.newClient
/home/tyk/go/src/github.com/getsentry/raven-go/client.go:304 +0x193
goroutine 6 [syscall, 10 minutes]:
os/signal.signal_recv(0x0)
/usr/local/go/src/runtime/sigqueue.go:116 +0x132
os/signal.loop()
/usr/local/go/src/os/signal/signal_unix.go:22 +0x18
created by os/signal.init.1
/usr/local/go/src/os/signal/signal_unix.go:28 +0x37
goroutine 7 [select]:
github.com/pmylund/go-cache.(*janitor).Run(0xc82013b0f0, 0xc8201277a0)
/home/tyk/go/src/github.com/pmylund/go-cache/cache.go:946 +0x13e
created by github.com/pmylund/go-cache.runJanitor
/home/tyk/go/src/github.com/pmylund/go-cache/cache.go:964 +0x81
goroutine 8 [sleep]:
time.Sleep(0x2540be400)
/usr/local/go/src/runtime/time.go:59 +0xf9
main.(*HostCheckerManager).CheckActivePollerLoop(0x11f1da0)
/home/tyk/go/src/github.com/lonelycode/tyk/host_checker_manager.go:120 +0x48b
created by main.(*HostCheckerManager).Start
/home/tyk/go/src/github.com/lonelycode/tyk/host_checker_manager.go:81 +0x3f
goroutine 106 [select, 10 minutes]:
github.com/lonelycode/gorpc.clientWriter(0xc8201a9680, 0x7f6a6c85b088, 0xc820022668, 0xc8202ede60, 0xc8202afaa0, 0xc82025bd40, 0xc82025bda0)
/home/tyk/go/src/github.com/lonelycode/gorpc/client.go:613 +0xa6b
created by github.com/lonelycode/gorpc.clientHandleConnection
/home/tyk/go/src/github.com/lonelycode/gorpc/client.go:560 +0x5de
goroutine 81 [select, 10 minutes]:
github.com/lonelycode/gorpc.clientWriter(0xc8201a9680, 0x7f6a6c85b088, 0xc8202bc1f0, 0xc8202d9b30, 0xc8202d6bd0, 0xc820390360, 0xc8203903c0)
/home/tyk/go/src/github.com/lonelycode/gorpc/client.go:613 +0xa6b
created by github.com/lonelycode/gorpc.clientHandleConnection
/home/tyk/go/src/github.com/lonelycode/gorpc/client.go:560 +0x5de
goroutine 20 [select]:
github.com/pmylund/go-cache.(*janitor).Run(0xc8202d6490, 0xc8202d86c0)
/home/tyk/go/src/github.com/pmylund/go-cache/cache.go:946 +0x13e
created by github.com/pmylund/go-cache.runJanitor
/home/tyk/go/src/github.com/pmylund/go-cache/cache.go:964 +0x81
goroutine 21 [chan send, 10 minutes]:
github.com/jeffail/tunny.(*workerWrapper).Loop(0xc8202d8720)
/home/tyk/go/src/github.com/jeffail/tunny/worker.go:51 +0xbc
created by github.com/jeffail/tunny.(*workerWrapper).Open
/home/tyk/go/src/github.com/jeffail/tunny/worker.go:80 +0x182
goroutine 22 [chan send, 10 minutes]:
github.com/jeffail/tunny.(*workerWrapper).Loop(0xc8202d8750)
/home/tyk/go/src/github.com/jeffail/tunny/worker.go:51 +0xbc
created by github.com/jeffail/tunny.(*workerWrapper).Open
/home/tyk/go/src/github.com/jeffail/tunny/worker.go:80 +0x182
goroutine 23 [chan send, 10 minutes]:
github.com/jeffail/tunny.(*workerWrapper).Loop(0xc8202d8780)
/home/tyk/go/src/github.com/jeffail/tunny/worker.go:51 +0xbc
created by github.com/jeffail/tunny.(*workerWrapper).Open
/home/tyk/go/src/github.com/jeffail/tunny/worker.go:80 +0x182