The most common reason is the tech has Fieldwork location services set for Only when using Fieldwork. When set for Only when using Fieldwork, and the tech exits the app, the tech is 'frozen' at that location until the tech reopens the app later in the day.
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For more information about enabling location services, see Mobile Location Settings - how to enable
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Is the tech turning off the phone in between jobs? The tech will show as being where he/she was when the phone was turned off. When the phone comes back on the pin in the Calendar map is updated.
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It the tech in an area where the signal drops out?
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Search the Internet to see how good the carrier's reception is in that area.
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Is the tech deep inside a building surrounded by cinder block walls? No signal leaves the building.
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Is the area rural or is the tech in a new housing development?
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Google sometimes has difficulties with mapping rural areas or quickly mapping new developments. Go on a real estate website and enter the address; if it's a new development Google might not have that information yet.
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Does the tech have a consistent area to work in?
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If the tech is in new territory numbers 1 and 2 above could apply, or the tech could just be lost.
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If it's just happening now and it hasn't happened before, it could be Google is having server issues, or more likely, Google is not refreshing as fast as it usually does.
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Is the tech hanging out at a location (Burger King?) for a very long time?
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Verify that location settings are not being changed on the mobile device.
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If the pin drop hasn't moved in some time it could be the tech left the device behind (Starbucks?).