If there is some string inserted into
...\components\com_community\templates\MyTheme\layouts\stream\status.php
as joomal string
JText::_('SOMETEXT')
and then that Joomla constant defined in language file of active joomla template, when new posts are loaded and displayed on wall instead of language string, constant is displayed (SOMETEXT).
When searching for language override in Joomla back-end string can be found via value or constant, so template language file is loaded, and working for initial batch of wall posts.
Everything works as it should if language override is created in Joomla backend for same constant with same value.

Hi Vladimir,

I dont really understand with your issue, if possible please provide me the screenshot, also we need your backend and FTP access.

thank you!

Sorry, but my site is still in development phase so I cannot provide you with back-end/ftp access.
How to replicate:
1) Make ...\components\com_community\templates\jomsocial\layouts\stream\status.php line 59 that looks like:
<div class="joms-stream__header">
to look like
<div class="joms-stream__header"><?php echo JText::_('MY_TEST_J_CONSTANT'); ?>
2) Add constant to Joomla template language file:
...\templates\protostar\language\en-GB\en-GB.tpl_protostar.ini
MY_TEST_J_CONSTANT="TEST STRING"
3) Reload wall. First batch of activities are looking fine. After loading more activities, on scroll, constant will appear instead of value.
4) Go to Joomla back-end and define language override for constant MY_TEST_J_CONSTANT and value TEST STRING.
5) Reload wall. Now newly loaded activities, on scroll, will have correct string displayed.
It is not big of a deal, since is can be fixed but still a bug :)

You put the string on wrong place, if you wanna put on .ini file please you put inside file en-GB.com_community.ini, but if you put on language override that is better and proper solution :)