Update: I was able to make the subfolders appear in the web client using the grommunio.x86_64-latest.install.iso.
Using developer tool in the browser i saw this
"grommunio-debug.js:72954 Uncaught RangeError: Incorrect locale information provided
at Intl.Collator (<anonymous>)
at constructor.compareRecordProp (grommunio-debug.js:72954:39)
at constructor.hierarchySort (grommunio-debug.js:72871:15)
at ext-base-all.js?version=3.9.140.g0a608be8-lp155.144.3:21:8903
at Array.sort (<anonymous>)
at constructor.sort (ext-base-all.js?version=3.9.140.g0a608be8-lp155.144.3:41:475299)
at constructor.sort (ext-base-all.js?version=3.9.140.g0a608be8-lp155.144.3:41:481596)
at constructor.doSort (extjs-mod-debug.js:4493:10)
at h.Event.fire (ext-base-all.js?version=3.9.140.g0a608be8-lp155.144.3:41:3699)
at constructor.fireEvent (ext-base-all.js?version=3.9.140.g0a608be8-lp155.144.3:41:687)"
I went into settings and set the language to "en_US" and voilá