Ultimaker had issues with there filament for a while where if you left it in the machine overnight or sometimes when printing it would break. you can test this by cutting 1m off the roll and taping it every 200mm in a straight line. the next day if its broken then you have a bad roll.
This is not normal for PLA and should remain strong. Sometimes old rolls can have some issues also.
you can get some temporary success by either heating the roll in the oven at 70deg for 30mins or putting it in how water and letting to dry before you print. You can search how to do this properly.
Ultimaker PLA is now good and without these problems, colorfabb, diamond age and faberdashery are all good brands of PLA also