Intensity minutes wrong last 7 days.

My Garmin Forerunner 735XT has started messing up intensity minutes.

On Mon 12Feb2024 I did a 63 minute ride and it gave me 61 intensity minutes (all good).

On Tue 13Feb2024 I did an 18 minute run and it gave me 20 intensity minutes (all good).

On Wed 14Feb2024 I did no recorded activity but it gave me 13 intensity minutes.

On Thu 15Feb2024 I did a 31 minute run and it gave me 68 intensity minutes.

On Sat 17 Feb2024 I did a 62 minute ride and it gave me 128 intensity minutes.

On Mon 19Feb2024 I did a 68 minute ride and it gave me 138 intensity minutes.

On Tu 20Feb2024 I did a 31 minute run and it gave me 112 intensity minutes.

From above, problem started Wed 14Feb2024.

Was there a software upgrade ? to either Garmin735XT or to iOS app ?
Settings shows current version is 4.62.1.3.