Focusing is one of the most difficult parts for every digital camera. Special on the end of the moon, and if the lights are low. Every camera needs sharp contrasting backgrounds and no distracting other high contrast objects in the foreground.
Be aware when you soon in to the end of the zoom range, you can't focus on close objects. Minimum focus distance can be a few meters.
It could be you switched to silence the focus noise, what can be bad for focusing.
See what the manual is telling you about zoom and focus:
Read the manual again, and check what settings would be the best for you while shooting video with a long zoom setting.
Here is the manual:
http://downloadcenter.samsung.com/content/UM/201405/20140522111801989/WB1100F_UM_English.pdf
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