TYPO3 Core

Are there any hints in the typo3_*.log log files in typo3temp/var/logs/?

Workaround :
Add the new URL in the TrustedHostPattern variable

What is the "new URL", and what has been the value before?
Did you try putting the names in in braces, like 'trustedHostsPattern' => '(first\.example\.org|second\.example\.org)'?

Hi,
as written in the description :

TrustedHostPattern value was (in v10 before upgrade) :

'trustedHostsPattern' => 'smto-typo.acc.internal.tld|app.smto-typo.acc.internal.tld|lb.smto-typo.acc.internal.tld|rp.smto-typo.acc.internal.tld|www.qual.external.tld|www.acc.external.tld'

TrustedHostPattern expected in the "Whoops" 

'trustedHostsPattern' => 'app.www.acc.internal.tld',

internal.tld and external.tld are "censored" placeholder of my real domains.

I may add that the typo site is behind a reverse proxy. The public available url site is www.acc.external.tld. It was called by the reverse proxy with app.smto-typo.acc.internal.tld but it seems after v11 it expect to be called on app.www.acc.internal.tld.

Did you try putting the names in in braces ? -> No backslash were added in the TrustedHostPattern in V10 and it was working. If I recall well, I did try to add backslash before dot in v11 but I still got a "Whoops".