Elgg 1.8 will NOT work on PHP 7!!!!

You need to upgrade at least to Elgg 2.3 to be able to run it on PHP 7. You need to upgrade to Elgg 2.3 when your server still runs on PHP 5.6 because only with version 2.3 Elgg became compatible with PHP 7 (while Elgg 2.3 still working with PHP 5.6).

And to make it clear: you can't upgrade directly from Elgg 1.8 to 2.3.

You need to upgrade from 1.8 to 1.9 then 1.10, 1.11 and 1.12. Only from Elgg 1.12 you should be able to directly upgrade to Elgg 2.3 then. Don't forget you also need to have compatible versions of 3rd party plugins matching to the Elgg version respectively.

Well, you had a few years to think about that I would say...

Also, some MySQL config tips

I am migrating my website to 8 GB RAM . The new php version will be php 7.2 instead of my current php 5.6 . Will my site work fine in php 7.2 .

Will my site work fine in php 7.2

Yes Elgg will work fine on newer versions of PHP. Unless you have a very old version of Elgg (like <2.3). In that case please update your Elgg installation ;)

Not sure what "Loop and Dynamic pointer" is supposed to be.

My guess is that the loss of the connection to your database is due to my.cnf settings with regard to the number of max connections and the keep-alive time of connections. Especially, if you are on a (cheap) shared server or "cloud server" hosting plan the coniguration of max connections is quite low and maybe most MySQL settings are kept on the default values even if they make not much sense. And you probably can't even make the necessary changes in my.cnf to stop the connection issues.

My advice: get in contact with the support of your webhoster to help you out optimizing the my.cnf settings (general advice is difficult because it depends also on things like memory available). And if you are not on a VPS or similar hosting plan you probably need to switch (and pay more...) to be able to make the necessary improvements.

1 - Check the read/write permissions on this folder

2 - Check the .htaccess rules on access to this folder

You can try these Q&A's:

http://elgghacks.com/questions/view/783/custom-html-js-and-css

http://elgghacks.com/questions/view/970/external-js-files

https://drive.google.com/file/d/14e94OOUmPiRx7zX48flN28ozXmxU4iep/view?usp=drivesdk

This is the link of the error .