"Import a series sale with empty required field" flakes: Element 'id:series-sale-url.errors' not visible in 5 seconds

[php-coder]

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FAIL: Robotframework.Series.Sales.Import.Validation.Import a series sale with empty required field
Element 'id:series-sale-url.errors' not visible in 5 seconds
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Seen there: https://travis-ci.com/github/php-coder/mystamps/jobs/483228119