Data mapper fails when editing already created integration

When I am trying to edit an integration that has a Data Mapper step, I see the mapped items from the source column duplicated below the initial "Document Root":

When I try to click this duplicated item, following happen:

And after about 5 seconds of not doing anything, this shows up:

In the developer tools console, there is this (which I believe is not any helpful, but still..)

ERROR TypeError: Cannot read property 'arguments' of null
    at Object.updateDirectives (atlasmap-vendor.js:21406)
    at Object.updateDirectives (atlasmap-vendor.js:14617)
    at yr (atlasmap-vendor.js:13749)
    at Mr (atlasmap-vendor.js:14038)
    at Or (atlasmap-vendor.js:14020)
    at yr (atlasmap-vendor.js:13749)
    at Mr (atlasmap-vendor.js:14038)
    at Or (atlasmap-vendor.js:14020)
    at yr (atlasmap-vendor.js:13749)
    at Mr (atlasmap-vendor.js:14038)

The integration pod log has no errors as well as the server log is not showing any error/exception.

When I try to edit the already created mapping, the source/target panel doesn't show anything (I can't select any multiplicity transformation or anything):

(Because I do a "SELECT * FROM contact WHERE first_name = 'SomeBody'", there is nothing really mapped when the integration runs, which is (I believe) because of this issue: https://issues.jboss.org/browse/ENTESB-11870 (Those issues are not related))