If it was scammed digitally, why can’t the funds be traced?
The details are here.
Reading through, it seems that the thieves took advantage of various weekend and public holiday bank closures, coupled with a breakdown of printers in Bangladesh. Some of the money was converted to cash (Pesos) but I suspect that they will recover more from the frozen accounts.
As I remember the story, the B. bank was skammed for almost a billion $. The thieves got away with 81 million. The rest of the money was stopped or recalled. The 81 million was transferred to the Philippines and then transferred to some local casinos. Conveniently local law provides that any money in the casino becomes untraceable. Helps with the tourist trade. 
So once the 81 million hit the casinos, the money became real and disappeared.
The OP is timely. The SWIFT network was hit again by the same very sophisticated thieves. Where in Bangladesh the local system of checks and balances involved actual printouts-so the thieves disabled key printers so no one could check the transaction, in this second case the unnamed bank relied on PDF files for verification. The thieves installed malware in the PDF readers that was specific to the false transaction and anyone using the PDF reader would not see the false transaction but otherwise the document would be fine.