[VUE 2] RowExpander crash when filtering paged AjaxStore with syncDataOnLoad

[JockeLindberg]

Forum post

We're on 5.5.0

Using an AjaxStore's readUrl, the grid loads just fine initially. When filtering, the resulting reload of data causes this error stack trace:

TypeError: Cannot read properties of undefined (reading 'type')
    at RowExpander.onStoreChange (https://local.BLAH.io/js/vue-app.js:85286:113)
    at AjaxStore.trigger (https://local.BLAH.io/js/vue-app.js:5819:34)
    at AjaxStore.onModelChange (https://local.BLAH.io/js/vue-app.js:28850:10)
    at ModelClass.afterChange (https://local.BLAH.io/js/vue-app.js:20295:13)
    at ModelClass.inSet (https://local.BLAH.io/js/vue-app.js:20259:10)
    at ModelClass.set (https://local.BLAH.io/js/vue-app.js:20128:25)
    at https://local.BLAH.io/js/vue-app.js:27830:35
    at Array.forEach (<anonymous>)
    at AjaxStore.syncFlatDataset (https://local.BLAH.io/js/vue-app.js:27816:10)
    at AjaxStore.syncDataset (https://local.BLAH.io/js/vue-app.js:27719:107)

Here is the chunk of code for RowExpander.onStoreChange, it's the source.modelClass.fieldMap[changedKeys[0]].type that is throwing the error

onStoreChange({ action, source, records, changes }) {
    var _a2;
    const me = this, { recordStateMap, collapsingStateMap } = me, changedKeys = changes && Object.keys(changes);
    if ((changedKeys == null ? void 0 : changedKeys.length) === 1 && source.modelClass.fieldMap[changedKeys[0]].type === "store") {
      return;
    }

It displays the error on screen, too, which makes it impossible to simply ignore and move on. The new data is displayed just fine in the grid.

What else do you need from me to troubleshoot/reproduce?