Posts face many crashes

I'm trying to publish this article for example "Quels produits utiliser pour protéger un revêtement extérieur en pruche?" (This happens with many other articles).

I encounter several type of crash.
1- The text I try to put on my welcome page duplicate and I can't remove it. In fact, it keep multiplying until the article completely crash and I can't update it anymore
<p>(Some text...)
<hr id="system-readmore" />
<p>(Same text that repeat...)
<hr id="system-readmore" />
<p>(Same text that repeat again if I try to update...)
<hr id="system-readmore" />

2- I'm trying to add a link. For some article, it is okay, for other article, it makes the article to crash, like in the article I take in example.
<p>L’<a href="catalog?produitno=579" target="_blank" rel="noopener noreferrer">huile pour terrace ALIS 579</a> et (... text continue)

3- The permanent link crash (quels-produits-utiliser-pour-proteger-un-revetement-exterieur-en-pruche-1)
Even though, I can't find the article (quels-produits-utiliser-pour-proteger-un-revetement-exterieur-en-pruche), I can't use the permanent link without the "1" at the end.

4- Another permanent link crash (quels-produits-utiliser-pour-proteger-un-revetement-exterieur-en-pruche-1)
Now, if I want to make another article (quels-produits-utiliser-pour-proteger-un-revetement-exterieur-en-pruche-2), the system doesn't allow me to do so. It come back to "1" and the article "1" crash and does not save. I kind of screwed here.

5- Some character appears and can't be removed when I add a picture
When adding this picture <img class="easyblog-image-caption" title="JM Tradition" src="images/easyblog_articles/42/b2ap3_large_JM-Tradition.png" width="424" height="308" align="center" data-style="clear" /><br /><span style="font-size: 12.16px;">
some characters like these appear at the end of my post. """"""""""""""""
Again, when I remove them, they reappear when I save my draft.