User storage is cleared when prompting for required parameter - actions-on-google

Question

I have a simple Welcome intent that contains a single required parameter. I am also using user storage to store a GUID for the current user, so they can come back and resume the conversation at a later stage.
This works fine if my Welcome intent doesn't contain a required parameter, i.e. the user can stop the conversation and come back much later, invoke the action again, and the user storage is still there.
But with the required parameter, the question that prompts for the value of that parameter appears to clear the user storage, so I no longer recognise the user. Is this expected/ how do I work around this (without using account linking)?
This is from the logs:
the initial invocation still contains the user storage values:
Sending request with post data: {"user":{"locale":"en-US","lastSeen":"2019-08-09T13:25:39Z","userStorage":"{\"data\":{\"userId\":\"23676205-5964-158d-44d0-c949ea01f6cc\"}}","userVerificationStatus":"VERIFIED"},"conversation":{"conversationId":"ABwppHG4dZXBOH0w3hbA8diwssTMi0z6uXvNcvzYFlJgAXW0ShoxhAQolhCP9Zq1TRxW8NxRyAl0V6GEDdrrLCMUkZST","type":"NEW"},"inputs":[{"intent":"actions.intent.MAIN","rawInputs":[{"inputType":"KEYBOARD","query":"Talk to IPSOS Diary Demo"}]}],"surface":{"capabilities":[{"name":"actions.capability.SCREEN_OUTPUT"},{"name":"actions.capability.MEDIA_RESPONSE_AUDIO"},{"name":"actions.capability.ACCOUNT_LINKING"},{"name":"actions.capability.AUDIO_OUTPUT"},{"name":"actions.capability.WEB_BROWSER"}]},"isInSandbox":true,"availableSurfaces":[{"capabilities":[{"name":"actions.capability.WEB_BROWSER"},{"name":"actions.capability.AUDIO_OUTPUT"},{"name":"actions.capability.SCREEN_OUTPUT"}]}],"requestType":"SIMULATOR"}.
the agent then sends back one of the prompt questions defined for the required parameter in the welcome intent:
Received response from agent with body: HTTP/1.1 200 OK Server: nginx/1.13.6 Date: Fri, 09 Aug 2019 13:25:48 GMT Content-Type: application/json; charset=utf-8 X-Content-Type-Options: nosniff google-actions-api-version: 2 Cache-Control: no-cache, no-store, max-age=0, must-revalidate Pragma: no-cache Expires: Mon, 01 Jan 1990 00:00:00 GMT P3P: CP="This is not a P3P policy! See g.co/p3phelp for more info." Content-Security-Policy: script-src 'report-sample' 'nonce-B8FmozDlPwPnGpgtItuU8A' 'unsafe-inline';object-src 'none';base-uri 'self';report-uri /_/DialogflowRuntimeAogHttp/cspreport;worker-src 'self' Content-Encoding: gzip X-XSS-Protection: 0 X-Frame-Options: SAMEORIGIN Set-Cookie: NID=188=wmvmHPvwa5ROoJQ5xNgLzzXmo4qPq4yyAX44A2ix7o0Vy2mgwiKJT92Th8KQtmz2YNBJWdx7W4pT_v610J-y1LRKig-NqHcpqJp8uLk84L-fnqBn2m7HIfvUlMDwb-SnwakZmcPu6SRKBBsS_FcXINYZ83ydJToyY-df3CxBAfg; expires=Sat, 08-Feb-2020 13:25:48 GMT; path=/; domain=.google.com; HttpOnly Via: 1.1 google Alt-Svc: clear Transfer-Encoding: chunked { "conversationToken": "[\"e8b7f358-3964-477c-a161-11da9d90e6bb_id_dialog_context\",\"default_welcome_intent_dialog_context\",\"default_welcome_intent_dialog_params_surveyname\",\"actions_capability_screen_output\",\"actions_capability_media_response_audio\",\"actions_capability_account_linking\",\"actions_capability_audio_output\",\"actions_capability_web_browser\",\"google_assistant_input_type_keyboard\",\"google_assistant_welcome\"]", "expectUserResponse": true, "expectedInputs": [{ "inputPrompt": { "richInitialPrompt": { "items": [{ "simpleResponse": { "textToSpeech": "Which survey is it?", "displayText": "Which survey is it?" } }] } }, "possibleIntents": [{ "intent": "assistant.intent.action.TEXT" }], "speechBiasingHints": ["$surveyname", "$surveyname"] }], "responseMetadata": { "status": { "message": "Success (200)" }, "queryMatchInfo": { "intent": "e8b7f358-3964-477c-a161-11da9d90e6bb" } }, "expectedInput": { "requestedIntent": { "intent": "e8b7f358-3964-477c-a161-11da9d90e6bb", "parameterName": "surveyname" } } }.
but when I get the response to the above prompt question, the user storage is now non-existent:
Sending request with post data: {"user":{"locale":"en-US","lastSeen":"2019-08-09T13:25:39Z","userVerificationStatus":"VERIFIED"},"conversation":{"conversationId":"ABwppHG4dZXBOH0w3hbA8diwssTMi0z6uXvNcvzYFlJgAXW0ShoxhAQolhCP9Zq1TRxW8NxRyAl0V6GEDdrrLCMUkZST","type":"ACTIVE","conversationToken":"[\"e8b7f358-3964-477c-a161-11da9d90e6bb_id_dialog_context\",\"default_welcome_intent_dialog_context\",\"default_welcome_intent_dialog_params_surveyname\",\"actions_capability_screen_output\",\"actions_capability_media_response_audio\",\"actions_capability_account_linking\",\"actions_capability_audio_output\",\"actions_capability_web_browser\",\"google_assistant_input_type_keyboard\",\"google_assistant_welcome\"]"},"inputs":[{"intent":"actions.intent.TEXT","rawInputs":[{"inputType":"KEYBOARD","query":"baby diary"}],"arguments":[{"name":"text","rawText":"baby diary","textValue":"baby diary"}]}],"surface":{"capabilities":[{"name":"actions.capability.SCREEN_OUTPUT"},{"name":"actions.capability.MEDIA_RESPONSE_AUDIO"},{"name":"actions.capability.WEB_BROWSER"},{"name":"actions.capability.AUDIO_OUTPUT"},{"name":"actions.capability.ACCOUNT_LINKING"}]},"isInSandbox":true,"availableSurfaces":[{"capabilities":[{"name":"actions.capability.SCREEN_OUTPUT"},{"name":"actions.capability.WEB_BROWSER"},{"name":"actions.capability.AUDIO_OUTPUT"}]}],"requestType":"SIMULATOR"}.