the driver used in LibreELEC for legacy nvidia cards is version 304.xx. As discussed on the parent/sister project forum, this has several drawbacks for users of ION/ION2 chipsets. Link:
I tested both versions, and while both offer hardware-accelerated playback with the ION chipset, only the 340.xx versions worked properly with European DVB-S and DVB-S2 broadcast streams (high-bitrate interlaced/progressive MPEG-2 576i/576p, high-bitrate progressive h.264 720p and very high-bitrate interlaced h.264 1080i). Problems are most noticeable with hardware deinterlacing turned on. Using HDMI passthrough with my AVR also worked better with the 340.xx version.
Regular local or remote HD/SD progressive material (internet streaming, MKV files) work fine with both versions.
Switching from version 304.xx to 340.xx would leave users of GeForce generation 6 and 7 cards without support, but these cards do not even offer any hardware accelerated playback of videos.
I would also like to mention that nvidia does not officially support the use of hardware accelerated video playback using vdpau on the 304.xx version.