this seems to work for patches

app/Http/Controllers/Api/AssetsController.php

@@ -556,7 +556,7 @@ public function store(StoreAssetRequest $request): JsonResponse
  $model = AssetModel::find($request->input('model_id'));
 
  // Check that it's an object and not a collection
- // (Sometimes people send arrays here and they shouldn't
+ // (Sometimes people send arrays here and they shouldn't, unless it's a checkbox)
  if (($model) && ($model instanceof AssetModel) && ($model->fieldset)) {
  foreach ($model->fieldset->fields as $field) {
 
@@ -657,18 +657,21 @@ public function update(ImageUploadRequest $request, $id)
  // Update custom fields
  if (($model) && (isset($model->fieldset))) {
  foreach ($model->fieldset->fields as $field) {
+ $field_val = $request->input($field->db_column, null);
  if ($request->has($field->db_column)) {
  if ($field->field_encrypted == '1') {
  if (Gate::allows('admin')) {
- $asset->{$field->db_column} = \Crypt::encrypt($request->input($field->db_column));
+ $asset->{$field->db_column} = Crypt::encrypt($field_val);
  }
- } else {
-  if ($field->element == 'checkbox') {
-  if(is_array($field_val)) {
-  $field_val = implode(',', $field_val);
- }
+ }
+ if ($field->element == 'checkbox') {
+ if(is_array($field_val)) {
+ $field_val = implode(',', $field_val);
+ $asset->{$field->db_column} = $field_val;
  }
- $asset->{$field->db_column} = $request->input($field->db_column);
+ }
+ else {
+ $asset->{$field->db_column} = $field_val;
  }
  }
  }