After upgrade from YAMLForm: "undefined function webform_schema()"

I've tried the YAML Form to Webform upgrade, and was using drush.

The upgrade itself seems to have gone OK (The webforms seem to be showing correctly on the site), but my system is now claiming it needs to do about 75 schema updates to webform.

If I use "drush up" to update, I get the following error:

Error: Call to undefined function webform_schema() in                [error]
webform_update_8008() (line 165 of
***/modules/webform/includes/webform.update.inc)

(***'s mine)

I have webform-8.x-5.0-beta1 installed, but if I do a "grep -r webform_schema", the function doesn't appear to be defined:

$ grep -r "webform_schema"
includes/webform.update.inc:  $schema = webform_schema();

The only thing I can think of was that I was following the drush instructions to the letter, and may have upgraded from webform-8.x-5.x-dev to webform-8.x-5.0-beta1 while I was running the site upgrade.

I've just done this update on a test site, so there's no great urgency, but I think I want to hold off on my live yamlform->webform upgrade until I can get this working!