[ads] sometimes tab events are not processed after browser restart

[btlechowski]

Description

Follow up to https://github.com/brave/brave-browser/issues/38373

Steps to reproduce

1. Clean profile
2. Run Brave with

--enable-logging=stderr --vmodule="*/variations/*"=6,"*/bat-native-ledger/*"=6,"*/brave_rewards/*"=6,"*/bat-native-ads/*"=6,"*bat-native-confirmations/*"=6,"*/brave_ads/*"=9,"*/brave_user_model/*"=6,"*/bat_ads/*"=6,"*/whats_new/*"=9 --variations-server-url=https://variations.bravesoftware.com/seed1 --rewards=staging=true,debug=true --use-dev-goupdater-url --enable-features=ShouldAlwaysRunBraveAdsService,ShouldAlwaysTriggerBraveSearchResultAdEvents,ShouldLaunchBraveAdsAsInProcessService,ShouldSupportSearchResultAds,ShouldAlwaysTriggerBraveNewTabPageAdEvents,CustomNotificationAds,NotificationAds:default_ads_per_hour/5,InlineContentAds:maximum_ads_per_day/1

3. Open NTP
4. Open brave.com in the tab
5. Restart browser
6. Check logs for Created tab with id and Tab id did become focused

Actual result

Events are not processed

Expected result

Events are processed

Reproduces how often

Easily reproduced

Brave version (brave://version info)

Brave	1.68.29 Chromium: 125.0.6422.60 (Official Build) nightly (64-bit)
Revision	00e032de86c92faa949ed70f87fa29f9ef10aad6
OS	Linux

cc @tmancey @aseren