Seems to be incompatible with CF7 version 5.5.3

After updating CF7 to version 5.5.3, forms that were previously set to be enabled for mailster are no longer enabled and no changes made on the mailster tab for the form can be saved. For example, if you click the toggle for “Enabled this form for Mailster” and then click the save button, when the page re-loads, the toggle is then un-checked.