Enable debug mode and check what queries are being made. That should help identify the issue.

Maybe this is the source?

The query's right. For your filter it is looking for titles containing 5837. If you want to look it up by ID, use id:5837 in the filter box (the same way most core components work).

Generally I consider requiring additional perimeters for a search field questionable for UI/UX.
An OR in the query should allow for searching by either title or ID without needing the additional prefix.
There is also no tool tip or other information specifying the necessity of a prefix for ID searching.

Generally speaking I doubt most people are searching core components by ID, although the tool tip does specify the prefix as an option.

Adding a tool tip to explain the use of the id: prefix and maybe changing lin 131 in the model PullsModel.php
from if (stripos($search, 'id:') === 0) to something like if (stripos($search, 'id:') === 0 || is_numeric($search))

It was done differently before (see 76de180 which changed it to follow the core convention), but that caused issues too. Updating the tooltip or adding the is_numeric check isn't a major issue I'd say.