The emails of the WordPress users are blocked by the spam filter !?

I have several WordPress sites. And a problem with one.

I just wanted to check if it is something ordinary, it happens to all, or if I should insist that the problem be solved. It's here:

The configuration is as follows, two websites in two different languages, each with their own cPanel and standalone WordPress installation, but configured in the same way (plugins, theme, design, everything), with the exception of the language . Say they are:

example.com (Croatian version)
english.example.com (obvious)

When a visitor wishes to register on my website ("subscribe"), he receives the following confirmation email (after entering his username and email address):

User Name: WHATEVER_VISITOR_CHOSE

To set your password, visit the following address:

https://english.example.com/wp-login.php

And it works perfectly for the English website.
However, the Croatian website sends (almost) exactly the same message, only in "Croatian". So it's like

Korisničko ime: WHATEVER_VISITOR_CHOSE

Za postavljanje lozinke, idite na sljedeću adresu:

The rest is the same (links), only with example.com, instead of english.example.com.

These messages are blocked by the hosting provider's spam filter (only Croatian, English are sent well). I can ask technology. support to "release" them, but I would rather not have to do it.

Is this a normal thing?
The fact that the confirmation emails are almost the same (only the user name differs) and do not have an "unsubscribe" link, does this often make them treated as spam?

In other words: is it reasonable that I expect the hosting provider to "fix" this? And if they do not, is it reasonable to expect that these problems will not arise at most hosting providers (reputable, good quality), so that I can try / hope that the change of hosting provider could solve the problem?

Technical Support has suggested modifying the contents of the email confirmation, adding an "unsubscribe" link and modifying the text a bit.
This would use another WordPress plugin, or the changing of the child theme functions.php (I think, I do not know how to do it exactly, it should be understood).
If it is common for these emails to be considered spam, there is no other way, I suppose. However, I have doubts:
– In the last three years (2 different hosting providers) this has not been a problem.
– If this is the case, most WordPress owners take care of this problem and modify the email form; I have never heard of it (it may just be misinformed, which is why I am asking the question here).

Thank you in advance for any help and info.

The accommodation will review, maybe solve, we'll see. I just want to see if my "insistence" about it was reasonable (or rude?) And what would be my options if it was not resolved.