Error: ***The value for "hamburgerCallback" must not be undefined

Same here. Last night (NZ time), everything worked, this morning I get those two exceptions about hamburgerCallback and InvalidOperation. I am  using MS Code and am developing an SPFx client webpart. I run it on the host-workbench: https://ourorganisation.sharepoint.com/sites/mainsite/subsite/_layouts/15/workbench.aspx . After "ignoring"/F5 the exceptions, it seems to run sweet.

Error: ***The value for "hamburgerCallback" must not be undefined
   at Function.e.isNotNullOrUndefined (https://spoprod-a.akamaihd.net/files/sp-client-prod_2017-08-11.019/sp-webpart-workbench-assembly_en-us_1103575b589894e6f7c32232400ee52c.js:273:1058)
   at e.get [as hamburgerCallback] (https://spoprod-a.akamaihd.net/files/sp-client-prod_2017-08-11.019/sp-webpart-workbench-assembly_en-us_1103575b589894e6f7c32232400ee52c.js:1276:17281)
   at e._onRender (https://spoprod-a.akamaihd.net/files/sp-client-prod_2017-08-11.019/sp-webpart-workbench-assembly_en-us_1103575b589894e6f7c32232400ee52c.js:1262:22876)
   at https://spoprod-a.akamaihd.net/files/sp-client-prod_2017-08-11.019/sp-webpart-workbench-assembly_en-us_1103575b589894e6f7c32232400ee52c.js:1262:22699
   at https://r1.res.office365.com/o365/versionless/shellcoreprimeg2m_1a333542.js:22:15411

 and:

Error: Sys.InvalidOperationException: Operation is not valid due to the current state of the object.
    at Function.Error.create (https://r1.res.office365.com/o365/versionless/shellcoreming2am_90c8efd1.js:65:13)
    at Function.Error.invalidOperation (https://r1.res.office365.com/o365/versionless/shellcoreming2am_90c8efd1.js:137:19)
    at Function._o365cl.a.b (https://r1.res.office365.com/o365/versionless/shellcoreming2am_90c8efd1.js:2479:12319)
    at _o365sg2c.r.b.f (https://r1.res.office365.com/o365/versionless/shellcoreprimeg2m_1a333542.js:20:1641)
    at _o365sg2c.r.a (https://r1.res.office365.com/o365/versionless/shellcoreprimeg2m_1a333542.js:20:858)
    at Function.O365Shell.InvokeSuiteAPILoaded (https://r1.res.office365.com/o365/versionless/shellcoreprimeg2m_1a333542.js:22:16618)
    at _o365sg2p.Loader.h (https://r1.res.office365.com/o365/versionless/shellplusg2m_90bca886.js:36:11288)