Two modules in the same position

Thx for answer, but that do not solves the problem I have.
On Jommla 3 and Helix Ultimate 2.0.7 I placed two modules in the same module position [feature] and aligned them side by side via css. Works great. Both modules are placed here within the div with id="sp-feature" .

<section id="sp-feature-bottom">
  <div class="row">
    <div id="sp-feature" class="col-lg-12 ">
      <div class="sp-column ">
        <div class="sp-module offset">
          <div class="sp-module-content">
            <div class="mod-article-single single mod-article-single__offset" id="module_155"> ........ </div>
          </div>
        </div>
        <div class="sp-module offset">
          <div class="sp-module-content">
            <div class="mod-article-single single mod-article-single__offset" id="module_153"> ........ </div>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>

If I do this on Joomla 4 and Helix Ultimate 2.0.11 the second module is placed here outside and after the div with id="sp-feature". The code looks so:

<section id="sp-feature-bottom">
  <div class="row">
    <div id="sp-feature" class="col-lg-12 ">
      <div class="sp-column ">
        <div class="sp-module article-single offset">
          <div class="sp-module-content">
            <div id="mod-custom212" class="mod-custom custom"> ........ </div>
          </div>
        </div>
      </div>
    </div>
    <div class="sp-module article-single offset">
      <div class="sp-module-content">
        <div id="mod-custom213" class="mod-custom custom"> ........ </div>
      </div>
    </div>
  </div>
</section>

As you can see, the 2nd custom module, which should actually be inserted inside the div with id="sp-feature", is only inserted after the closed div. Here, in my opinion, somehow faulty source code is generated.
I hope that I was able to describe the problem clearly.

Hi Christoph. If you allow...

I don't think this is a bug. Most likely you have a non -closed tag in one of your modules. But in any case, the reason can be determined only by accessing your site and using the code inspector. There is no other way to determine the cause.

You can check your modules in this way. Turn OFF them, instead, place two new ones with the same class article-single offset and with simple content, and see what will happen.

And one more thought. Сlasses like article-single , offset are a very common class names. This can be involved in Joomla or template files and affect your modules. Try to rename the classes. Always come up with the unique names of classes that are different from generally accepted terminological names.

Many developers use prefix to unique class names. For example, the JoomShaper team uses the prefix sp-. Come up with your prefix and use it.

Something like prfx-article-single, prfx-offset

Thank you for your helpful reply and shame on me.

In fact, I had a buggy code inside the custom module that was responsible for my problem.

Now I know that I was the problem ;-)