Malformed SOM expression: form1[0]ConcreteFieldReport[0].FooterFields[0].SignatureField1[0]

Open the form in LC, select form1 in the hierarchy, open the script window if it isn't already open (Window > Script Editor), change the view to show "Events with Scripts", press CTRL+F to open the find box, and type the expression in the "Find What" field. You'll probably have to leave out the indexes, and you'll likely only need the first part of it.

But how do I find the script?

You'll have to find the script that has the incorrect string and put it in.

How do I add that dot?

Add the missing dot.

xfa.resolveNode("form1[0].ConcreteFieldReport[0].FooterFields[0].SignatureField1[0]").rawValue = "something";

So what should I do to eliminate this problem?

This is the only way I can get that error in Acrobat. Notice that I left the dot out of the string between form1[0] and ConcreteFieldReport[0].

No, there is no dot missing

Is there a dot missing between the first index and Concrete?

form1[0].ConcreteFieldReport[0].FooterFields[0].SignatureField1[0]