Inconsistent URL Redirection Issue on Mobile Devices: Temporary Unavailability Error

Question

I have encountered an unusual issue with URL redirection on mobile devices, specifically related to the interaction between two sites hosted on Jelastic Cloud and using Let's Encrypt certificates. Here's a detailed explanation:

I have a WordPress website hosted at www.comtrax.ch, and it contains a login button that redirects users to an application hosted at https://app.comtrax.ch in a new tab. The redirection works perfectly fine on desktop computers. However, on mobile devices, I sometimes encounter an error message stating, "The page you are looking for is temporarily unavailable. Please try again later."

What's even more peculiar is that if I manually open https://app.comtrax.ch in the mobile browser first, and then navigate from www.comtrax.ch to https://app.comtrax.ch via the login button, the redirection works as expected.

I've made attempts to reproduce the issue consistently, but it appears to be intermittent. Sometimes the redirection works flawlessly, while other times it triggers the temporary unavailability error.

**Additional details: **

Both sites are running on Jelastic Cloud. Both sites are secured with Let's Encrypt certificates. app.comtrax.ch: Nginx + Frontend(Vue.js)

Oder wotsch dis ergänze mitem folgende text? Fallt dir nomeh sache i wo mir testet hend?

The steps we have taken to address the issues are as follows:

• We examined the issue using BrowserStack Live but were unable to reproduce the error message. We attempted to replicate it by testing different IP locations.
• We verified the redirect URLs specified as https://app.comtrax.ch.
• We cannot replace one of the CNAME-records pointing to the Wordpress site because it would interfere with the MX records.
• We confirmed the presence of an SOA entry record for our domain.
• We have verified that the wildcard subdomain record does not take precedence over the exact subdomain record

Our DNS landscape is structured as follows:

We have two A-records pointing from www.comtrax. ch and comtrax. ch to the IP address where our Wordpress page is hosted. Additionally, we have an A-record pointing from app.comtrax.ch to a different IP address.

**Reproduction Steps: **

1. Access www.comtrax.ch on a mobile device.

2. Click on the demo button.

3. Observe the issue: "The page you are looking for is temporarily unavailable. Please try again later."

Error Message

I would greatly appreciate any insights, suggestions, or troubleshooting steps to help identify the root cause of this inconsistent URL redirection issue on mobile devices. Thank you for your assistance.