[Elecraft] KAP1500 High SWR wen unkeying with FT8

[Ac9c]

Hi All - I'm new the this list after recently purchasing a used KPA1500. The KPA1500 has been working well on 6M with my IC7300. Last night it started indicating High SWR at the end of FT transmission when unkeying the amp.  The SWR of the antenna is 1.3:1 and the amp is fine during from keyup of each transmission up until the radio unkeys the amp.  I'm using the RCA to RCA keying line from the IC7300 to the KPA1500. Any ideas?
Mike Taylor AC9C