A way to disable rollup summary field

I don't know if there's a straightforward way to do that. But you could add a filter, so it won't calculate the new data. And then edit the field again and have it mass calculate everything

I do not know if there is a way to disable the Roll up field but you can be more strategic with your data loads to minimize the occurence

Order your loads by the master object’s record IDs; this strategy minimizes how often the records being updated in multiple, concurrent batches reference a single master record’s ID.

1.Which API are you loading the data ?

If the data volumes are huge use Bulk API and if are not worried about time it takes to load use Serial loading