Issue Definition

When the player is crossing the world grid border, the game checks for the possible events launch or preparation of such events. Some particular "service" quests (these quests are not in your quest journal) are activated for this and the process of initializing aliases in such quests begin. 

The location and references in these quests are dynamic, so with location initialization and with a search for a suitable reference start, the location condition (which alias is dynamic as well) may receive NULL, or be timed out, or there may be a general sequence failure.

The location alias resolving is delayed because of the fact that the game start to iterate all the grid formIDs from every mod that by one way or another interfere with this grid (the grid with abovementioned events). 

In other words, the more mods (plugins) that affect the same world grid with events, the higher the chance of CTD. The chance is extremely low on vanilla un-modded Skyrim and high enough on heavily modded game. Probably any of you faced this type of CTD when entering the Whiterun grid for example (many mods alter these grids): 
The same applies to grids near Solitude, Windhelm, Markarth and many others all over Skyrim. 

Solution

The solution is quite simple: place the location condition check under the faction condition check. In such case there will be enough time for the location alias to be successfully resolved. This is how it looks in xEdit: 



The same with another event-based quests. 

This approach was tested by me and some other players (tests were made with different mods setup, repeating grid transition), and it has proven to work (no CTDs when player transition the grid border anymore).

Compatibility 

This mod is compatible with any other bug fix mod.
There are two versions: with Unofficial Skyrim Legendary Edition patch dependency and without it. 

Some mods that contain edits of that event-based quests may conflict. This conflicts may be easily resolved in xEdit (see the image above). If you find any conflicting mod, please let me know, I may release a patch for it. 

Install with any preferred mod manager or just drop the plugin into Data folder and activate it in launcher. 

Plugin should be placed near the bottom of load order. To make sure everything is fine, check conflicts with xEdit. 

Version 2.0 contains BSA archive with some modified scripts (see changelog for explanation). There may be some file conflicts with other mods, keep in mind that loose files always have priority over files packed in BSA.

Credits 

All credit goes to Mitradis as it's he who managed to find a culprit of this issue (he asked me to upload this mod on Nexus).
If you have any questions, feel free to ask in the comment section.