J.P. Morgan Chase & Co. allegedly withheld a $12 million payment to Good Technology Inc. last year, worsening a cash shortage that forced the mobile-security company into a sale brokered by the bank, according to newly public claims in a continuing legal dispute.

The new details allege that the bank, in its capacity as a customer of Good Technology, hastened the company’s demise, even while the bank was advising it on a…