AltStore keeps asking for Apple ID (possibly due to email capitalization)

Describe the bug
With my Apple (Developer) ID, I always get asked to sign in when refreshing or installing an app.
-> Look at "additional context" for my theory of why this happens for some people.

To Reproduce
Steps to reproduce the behavior:

1. Refresh/Install new App
2. Getting login dialog

Expected behavior
Not getting a login dialog each time I try to refresh/install a new app.

Desktop (please complete the following information if applicable):

• OS: macOS
• Version: Catalina 10.15.5 (19F101)

iPhone (please complete the following information):

• Device: iPhone X (GSM)
• iOS: 13.5 (non jailbroken)

Additional context/Possible fix
I already saw a couple of users on Reddit talking about this issue.
When I originally created my Apple-ID, I had the default @icloud.com and only later changed it to my @gmail.com address. However, I probably capitalized two letters in that email.
On the appleid.apple.com website, it does show all lowercase though. Except in one place where I can actually see two letters capitalized. (German: "E‑MAIL-ADRESSE VERBERGEN
Weiterleiten an:" part (English rough translation: "Hide E-Mail. Forward to:")

This information is also shown in AltStore in the settings tab, when "logged in".

When I then refresh/install an app, I need to log in with all lower-case of my Apple-ID. (Else login fails).
However, it always sets the "Email" in the settings tab to the email with two letters capitalized.

I suppose that AltStore uses the email which is also displayed in the settings tab to log in each time and fails, as there are two letters capitalized.
Perhaps simply lower-casing that information (when sending to Apple or before saving the email) would be able to solve that issue.

(It does not seem (easily) possible to change my Apple-ID email to all lowercase, as Apple sees this as the same email?)

Edit: Perhaps the best solution would be that AltStore simply uses the email that was last entered by the user (and successfully signed in with) and use that (+ showing that in the AltStore settings tab)?

Start with the refresh/install login flow and the email shown in the AltStore settings tab, as described in the issue. Reproduce the repeated sign-in prompt and verify whether the address is normalized or the last successfully entered address is retained; done means refreshing or installing no longer repeatedly prompts for login.