Some features in a time-enabled hosted layer do not show up on a web map in ArcGIS Online

Error Message

Some features in a time-enabled layer are not visible on a web map when time animation is enabled, even when the time slider covers the whole timeframe,as shown in the following images.

Cause

Features are not displayed on the map that are missing dates and times in the attribute field that is used for the time animation in the feature layer, as seen in the following image.

Solution or Workaround

To resolve this, you may use any of the following workarounds:

1. Add dates for all features.
2. Change the time settings for the layer and use a different date field that has dates for all features.
3. Disable time animation.