Functions not running in single tick

It seems as though functions and other things are happening in a strange order compared to 1.12.

If I had a function that had 2 commands in it:

/execute as @e[type=item,tag=] at @s run setblock ~1 ~ ~ air destroy
/execute as @e[type=item,tag=] at @s run data merge entity @s {Tags:["Tagged"]}

Both the entity that currently is on the ground and the one just broken get a tag, and if this is run again the chain no longer continues.

Expected Behavior:
Only the first entity is given a tag, than the function finished and the item is created, allowing the next item to run the execute command.