One of our apps does most of its work in an NSOperation subclass, and most of the work involves sending hundreds of AppleScripts to InDesign. We only send them on the main thread via:dispatch_sync(dispatch_get_main_queue(), ^{ [self _runAppleScriptWithDict:infoDict];});Since upgrading from an old MacBook Pro running 10.10.x and whatever Xcode it could handle to a fairly new one running 10.13..6 and Xcode 10.1, I've been seeing a lot of problems when debugging, stopping at breakpoints, then either stepping or continuing when the next line involves sending an AppleScript on the main thread. The main thread looks like:#00x00007fff54fefaee in __psynch_rw_wrlock ()#10x0000000100e109a9 in _pthread_rwlock_lock_wait ()#20x0000000100e108f0 in _pthread_rwlock_lock_slow ()#30x00000001005ff39d in enter_stack_in_backtrace_uniquing_table ()#40x00000001005fb92e in gcd_queue_item_enqueue_hook ()#50x0000000100dbe085 in _dispatch_introspection_queue_item_enqueue_hook ()#60x0000000100da5794 in _dispatch_root_queue_push_override