The projection datum for user defined
(Proj4: +proj=longlat +a=6377301.243 +b=6356100.2284 +towgs84=295.00,736.00,257.00,0,0,0,0 +no_defs) works well in Qgis 2.18 but it does not work in Qgis 3.4 version.
in response to :Please provide with some details that prove your case. Some screen shots. – Vadym Here are some screenshots for reference. in fig 1, I open a layer in QGIS 3.4.4 which have WGS84/UTM44N projection.
in fig 5, the project projection changed in WGS 84 system instead of desired/selected CRS i.e. Modified UTM for central Nepal.
It works well in QGIS 2.18 Version but doesnot in QGIS 3.4.4. I use the MAC, Apple labtop.