Could you please provide a test case to reproduce it? We need more context. The only thing that I have in my mind now - you apply filter for main resourceStore in your code, so resource has not been deleted but filtered. I cannot be sure before debug your code.
If I am correct, the solution will be to use chained store for resourceList and not filter the initial store. https://bryntum.com/docs/scheduler-pro/api/Core/data/mixin/StoreChained
Checking you code and cannot understand what exactly are you trying to achieve.
I see find method now instead of filter, so I am not sure what's your goal.
From my comment above. resourceField uses original resourceStore by default. If you apply filter on combo's store, it will filter resources in your scheduler as well. To see resourceField with filtered set of resources, you need to use chained instance of resourceStore and apply filter on that instance instead.
const reqSkills = taskRecord.reqSkills; // just copied from your code
const resourcesField = editor.widgetMap.resourcesField; // easier to get resourcesField by it's reference name, instead of index
const resourceList = resourcesField.store.chain(); // create chained store
resourcesField.store = resourceList; // apply new instance of store to combo
resourceList.filter('skills', reqSkills); // filter chained store
Checking you code and cannot understand what exactly are you trying to achieve.
I see find method now instead of filter, so I am not sure what's your goal.
From my comment above. resourceField uses original resourceStore by default. If you apply filter on combo's store, it will filter resources in your scheduler as well. To see resourceField with filtered set of resources, you need to use chained instance of resourceStore and apply filter on that instance instead.
const reqSkills = taskRecord.reqSkills; // just copied from your code
const resourcesField = editor.widgetMap.resourcesField; // easier to get resourcesField by it's reference name, instead of index
const resourceList = resourcesField.store.chain(); // create chained store
resourcesField.store = resourceList; // apply new instance of store to combo
resourceList.filter('skills', reqSkills); // filter chained store