🚨 Error: Failed to execute 'animate' on 'Element': Partial keyframes are not supported.

Details
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**Error report:** [link](http://go/ampe/CM7q1ZqDodT0ngE)
**First seen:** Mar 24, 2019
**Frequency:** ~ 1,104/day

Stacktrace
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Error: Failed to execute 'animate' on 'Element': Partial keyframes are not supported.

    at animate (extensions/amp-animation/0.1/runners/native-web-animation-runner.js:85:36)

    at map (extensions/amp-animation/0.1/runners/native-web-animation-runner.js:80:35)

    at init (extensions/amp-animation/0.1/amp-animation.js:430:21)

Notes
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`@rsimha` modified `extensions/amp-animation/0.1/runners/native-web-animation-runner.js:85-86` in [#23417](https://github.com/ampproject/amphtml/pull/23417) (Jul 19, 2019)
`@renovate-bot` modified `extensions/amp-animation/0.1/runners/native-web-animation-runner.js:80-80` in [#27350](https://github.com/ampproject/amphtml/pull/27350) (Mar 30, 2020)
`@aghassemi` modified `extensions/amp-animation/0.1/amp-animation.js:428-436` in [#10818](https://github.com/ampproject/amphtml/pull/10818) (Aug 15, 2017)

**Seen in:**
- 05-15 Beta (0310)
- 05-15 Experiment-B (0310)
- 05-15 Experimental (0310)
- 05-15 Stable (0310)
- 05-21 Nightly (0438)
- +7 more

/cc @ampproject/release-on-duty