Ipsec DPD failure

running 2 FG 300D clusters and have a ipsec tunnel between them and worked flawless 6 months and yesterday i got DPD error and tunnel went down for 10 min and i saw in one Cluster i had CPU trap sent with high treshold.

running 5.2.8 on both clusters.

the link between them had no errors on interfaces

any hints ?

// Anders