objective c – flutter plugin does not execute background iOS code with lock

I have flutter plugin (https://github.com/mapp-digital/Mapp-Intelligence-Flutter-Tracking) which contains native iOS code background execution, which works fine until last update of Flutter version:
Flutter 3.16.3 • channel stable • https://github.com/flutter/flutter.git
Framework • revision b0366e0a3f (7 days ago) • 2023-12-05 19:46:39 -0800
Engine • revision 54a7145303
Tools • Dart 3.2.3 • DevTools 2.28.4

iOS part of code:

                     ^(void) {
                       // Background Thread
                       [self->_conditionUntilGetFNS lock];
                       while (!self->_isReady)
                         [self->_conditionUntilGetFNS wait];
                         [self enqueueRequestForEvent:event];
                         [self->_conditionUntilGetFNS signal];
                         [self->_conditionUntilGetFNS unlock];
                     });

this one line [self enqueueRequestForEvent:event]; is never executed.
what I can do?