[Forminator Pro] Forminator calculation stopped working

Hi! We have a “wedding cost calculator” on our site created with Forminator. It worked for a while now, but around last week one of the calculations stopped working. The form can be submitted and the email notification is sent, also the sum is visible while filling out the form, but once the email is sent, 2 calculated values in the e-mail give an error (they would calculate the sub-total and total costs). The error that shows up instead of the value is:
Error: Missing calculable subterm. Are there empty brackets?