WDL validates and runs fine standalone, but crashes when uploaded to Firecloud

I inherited a large block of WDL 1.0 It validates fine on womtool 32, 33.1, and 34, and I've tested that it runs fine on Cromwell 34. However, when I try to upload it to the method repo, via ether GUI or FISSFC, I get a WDL validation error:

Error 400 (FireCloud): Invalid WDL: Unrecognized token on line 653, column 23:

        -t ~{cpu} \
                  ^

Any idea what is happening or the best way to debug?
Gordon