The story
Possibly from shambles + -o- + -ic (adjective), in which the interconsonantal -o- avoids the /mbl/ consonant cluster. Possibly influenced by symbolic. Alternatively, possibly a blend of shambles + symbolic.
First known use, by meaning
- from 1952 Chaotic, disorganised or mismanaged.
Etymology from Wiktionary, CC BY-SA 4.0.