"use each line one time" along with "Only read" setting.
That way each thread will start new browser instance and
use new resource line because its set to use each line only
one time. When all proxies are used one time, script will
finish.
Just updated to 28.3.0 and now getting a "TypeError: Result of expression 'c._Break' [null] is not a function. during execution of action " on the "Set proxy" step in my script (created with 28.1.2 and updated in script editor of 28.3.0).
How can this be fixed?

yes we all encounter issue
@genericname1 Okay, I didn't know that :D Any workaround for this? Or can't I use proxies any longer in BAS ;)
revert to old
@genericname1 @morpheus93
How can this be repeated?
Send a screenshot, what parameters have you specified in the "Proxy" action?
Please attach the proxies with which the problem occurs here or in the forum's private messages
@genericname1 Could you send this to me too please?
@dda
How can this be repeated? If I create a new project, does this happen again?
Send a screenshot, what parameters have you specified in the "Proxy" action
Please attach the proxies with which the problem occurs in the forum's private messages