I created this demo multisport activity (run, HIIT, strength), when each 3 used my CIQ DF that records some data to FIT:
https://connect.garmin.com/modern/activity/8973862272?share_unique_id=24
When you open the link you'll see that there are 4 tabs: Multisport, Run, HIIT, Strength.
When you land on the above link you're in the Multisport tab, and you see a graph recorded by Connect IQ: ANT Heart Rate (bpm).
BUG 1: However when you change the tab to Multisport from any of the sub-activities' tabs, then the Connect IQ graph is not rendered any more.
The same is true for the Running tab: when you LAND on it using this link: https://connect.garmin.com/modern/activity/8973862272/1 (or open it in a new BROWSER tab/window using the icons in the web page) then you see both the Connect IQ graph and the Connect IQ stats.
BUG 2 & 3: However when you switch to the Running tab from any of the other tabs then neither the graph, nor the stats are displayed.
Possibly related to: https://forums.garmin.com/developer/connect-iq/i/bug-reports/hiit-and-strength-activity-doesn-t-display-all-the-recorded-fit-data