False Positives on 2 phones and misleading information about when the encounter happened

Avoid duplicates

• Bug is not mentioned in the FAQ
• Bug is specific for Android only, for general issues / questions that apply to iOS and Android please raise them in the documentation repository
• Bug is not already reported in another issue

Technical details

First device:

• Device name: Pixel 5
• Android version: Android 11
• App version: 1.9.1
• ENF Version: 18204713000
• Rooted: NO
• ENF LOG: all-exposure-checks-pixel3g.txt

Second device:

• Device name: Pixel 3a
• Android version: Android 11
• App version: 1.9.1
• ENF Version: 18204516000
• Rooted: NO
• ENF Log: all-exposure-checks-pixel5.txt

Describe the bug

Since yesterday, 23.12.2020 around 21:00 CEST the app shows on Pixel 3g that there was a high risk contact within the last 3 days.

Exact wording: “Sie haben ein erhöhtes Infektionsrisiko, da Sie zuletzt vor 3 Tagen mindestens einer nachweislich Corona-positiv getesteten Person über einen längeren Zeitraum und mit geringen Abstand begegnet sind”. See screenshot for that.

At the same time the app says - “Zuletzt am 15.12.20202”

This is confusing for the user, which information is now correct either 15.12. or the last 3 days?

Now since today, 24.12.2020 around 08:00 CEST the Pixel 5 shows “Begegnung an 4 Tagen mit erhöhtem Risiko” and “Zuletzt am 17.12.2020”. The detail text says:

“Sie haben ein erhöhtes Infektionsrisiko, da Sie zuletzt vor 4 Tagen mindestens einer nachweislich Corona-positiv getesteten Person über einen längeren Zeitraum und mit geringen Abstand begegnet sind”. See screenshot for that."

This is confusing for the user, which information is now correct either 17.12. or the last 4 days?

Now the next weird thing for Pixel 3g When looking through the ENA logs (attached above) you can see for Pixel 3g that it has 0! matchesCount except for ONLY ONE time on 23. Dezember 2020, 20:27 which shows up 5. Even after that it shows 0 which is as far as I can read from the other issues here on github is not how it works. How come there were 0 other matchesCount before and AFTER this date?

Same weird thing for Pixel 5: When looking through the ENA logs (attached above) you can see for Pixel 5g that it has:

• 1 match 17.12. 00:12 till 21.12. 15:17
• 0 matches between 21.12. 19:18 till 23.12. 19:50
• 5 matches exactly once on 24.12. 02:01
• 0 matches following after that for example on 24.12. 06:04

How is it possible, shouldn’t there be 5 matches also in the next checks until they “expire”?

Additional context

• On 17.12.2020 Pixel 5 was at all times isolated at home, no outside contacts whatsoever, how is it possible?
• On 15.12.2020 Pixel 3g was at all times isolated at home, no outside contacts whatsoever and also has 0 matches in ENF log, how come the app shows risk contact at that day?
• There seems to be a false positive report / server bug which shows 5 matches on both phones?
• If there is no bug and the information is correct - which one? The dates 17.12. and 15.12. or “the last 3/4 days”?
• Unfortunately both phones are not rooted so can not get more info here

Screenshots

Pixel 3g:

Pixel 5:

[MikeMcC399]

@tolzhabayev One of your issues regarding the conflicting information about when an encounter took place was already reported in https://github.com/corona-warn-app/cwa-app-android/issues/1964 which is labelled to be fixed in version 1.10.

[MikeMcC399]

@tolzhabayev

I think we can close this bug ticket for now but this behavior might unsettle some people who do not really understand how it works.

I’m sure you are right that the change in results may cause some people some worry. That was the reason for creating the FAQ article:

https://www.coronawarn.app/en/faq/#encounter_count_19

and for a deeper explanation:

https://www.coronawarn.app/en/faq/#encounter_19_calc

The change only happens once after the update to version 1.9 or later, then the calculation method stays stable.

Since you are the author, you can close the issue yourself if you want to, using the button at the bottom.