You probably send troops in one time with another player, he could be more closer to this tile or had better movement speed. Always check on global map, anybody else could send troops to this tile before you do it.

And about situation when you attacked another player with no warning pop up - when you send your troops and your city have no shield, your troop will automatic fight in tile if somebody else be there.

Hello, TLMPHATKAT 

To clarify this situation, please, provide us with the following information in private message:

1. Your game ID;

2. The exact time when you sent your troops on the tile;

3. The video illustrating your issue;

4. Screenshots of the Battle Reports.