It’s been sometime since initial 1.9 was published. Current version is 1.9.8. Main improvements since 1.8 are:
Support different layer styles
Each layer can contain different layer styles, which are stored in QGIS project. Default style is loaded on start and then user can select other style.
Display spatial bookmarks
QGIS allows creating spatial bookmarks, which can be stored locally or in project file. EQWC now supports reading project type spatial bookmarks.
QGIS Server 3.10 LTR
This release is prepared to work with QGIS 3.10 in most cases. Note that QGIS 3.10 Server has one open issue regarding printing external WMS layers. If you don’t need this feature, then 3.10 is safe to use, otherwise use 3.4 or wait for upcoming test of QGIS 3.16.
Map loading widget
Smart location tracking
Display legend for layers
Better error handling (alert icon and stored messages)
Dynamic printing of WMS base layers with support for external_wms parameter
Choose projection in web interface for displaying coordinates, for exporting data and in identify window
Support for nogeometry layers (plain tables)
Use tooltips and field templates in identify window
Support layers TMS format
Lot of minor fixes and changes
More information and code on GitHub.