LL_REJECT_EXT_IND caused high speed connection between iPhone 8 and DA14585

Dear Dlg Support,

We found that in some cases DA14585 and iPhone 8 can get stuck in high speed connection.

In our application, we try to maximize connection parameter to reduce power consumption. So a few seconds (6s) after a new connection, the slave (da14580/1/5) tries to issue connection parameter update request to increase connection interval to maximum value allowed.

It has bee working well on DA14580/581 in our products. However in the latest DA14585, it has issue interacting with iPhone 8 if more than 1 connection is made. The firmware is updated accordingly to use SDK6.0.6.509. Here is the scenario and we can reproduce it in many occasions without much difficulty:

Upon launching our iOS app, it will try to establish 2 connections with 2 da14585 (or one 14585 + one da14580) in serial, the da14585 in some occasions get stuck in the short connection interval while 14580 works well always.

If only one connection to da14585 using iPhone 8, it always work well.

Can you please help us to check if there is anything wrong in the 14585's dealing with connection parameter update?

The worst case, if we have to capture this abnormality so that we can terminate (time out) the high speed link so that iOS app can reconnect, do we have any hooks in the SDK to do so - say observe/capture the LL_REJECT_EXT_IND event and disconnect?

I hereby attached 4 sniff traces -
2 bad 585 traces - bad_585_connection_LL_REJECT_EXT_IND_1_more_than_1_connection and bad_585_connection_LL_REJECT_EXT_IND_2_more_than_1_connection
1 good one - Single 14585 card connection OK_always
1 good DA14580 trace - iOS app interact with 14580 OK always

Thanks for your support,
uta_lc