[MX Player] pcroland:
MX Player version: 1.8.3

"Enable embedded subtitles" option is enabled

neon.1.8.0 custom codec

Samsung Galaxy Note 3

DarkLord Note 5 ROM

Mediainfo log:

General
Unique ID : 250621722520498875122338231687094008256 (0xBC8BFCEE544130C7AC96F6600D8CF9C0)
Complete name : C:\Users\pc\Desktop\DL\The.Sopranos.S01-S06.COMPLETE.720p.BluRay.DD5.1.x264.HuN-TRiNiTY\The.Sopranos.S06.720p.BluRay.DD5.1.x264.HuN-TRiNiTY\the.sopranos.s06e01.720p-trinity.mkv
Format : Matroska
Format version : Version 4 / Version 2
File size : 3.13 GiB
Duration : 52mn 22s
Overall bit rate : 8 558 Kbps
Movie name : The Sopranos Season Six
Encoded date : UTC 2015-01-01 13:11:22
Writing application : mkvmerge v6.5.0 ('Isn't she lovely') built on Oct 20 2013 12:50:05
Writing library : libebml v1.3.0 + libmatroska v1.4.1

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 9 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 52mn 22s
Bit rate : 7 556 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.342
Stream size : 2.76 GiB (88%)
Writing library : x264 core 142 r2431+42 c69a006 tMod [8-bit@4:2:0 X86_64]
Encoding settings : cabac=1 / ref=9 / deblock=1:-3:-3 / analyse=0x3:0x113 / me=umh / subme=10 / psy=1 / fade_compensate=0.00 / psy_rd=1.10:0.00 / mixed_ref=1 / me_range=32 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-2 / threads=6 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=0 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / fgo=0 / bframes=10 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=60 / rc=crf / mbtree=0 / crf=17.0000 / qcomp=0.60 / qpmin=0:0:0 / qpmax=69:69:69 / qpstep=4 / vbv_maxrate=62500 / vbv_bufsize=78125 / crf_max=0.0 / nal_hrd=none / filler=0 / ip_ratio=1.30 / pb_ratio=1.20 / aq=2:0.70 / aq-sensitivity=10.00 / aq-factor=1.00:1.00:1.00 / aq2=0 / aq3=0
Language : English
Default : Yes
Forced : No

Audio #1
ID : 2
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 52mn 22s
Bit rate mode : Constant
Bit rate : 192 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Frame rate : 31.250 fps (1536 spf)
Compression mode : Lossy
Stream size : 71.9 MiB (2%)
Language : Hungarian
Default : Yes
Forced : No

Audio #2
ID : 3
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 52mn 22s
Bit rate mode : Constant
Bit rate : 640 Kbps
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 KHz
Frame rate : 31.250 fps (1536 spf)
Compression mode : Lossy
Stream size : 240 MiB (7%)
Language : English
Default : No
Forced : No

Text #1
ID : 4
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Language : Hungarian
Default : Yes
Forced : Yes

Text #2
ID : 5
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Language : Hungarian
Default : No
Forced : No

Text #3
ID : 6
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Language : English
Default : No
Forced : No

Menu
00:00:00.000 : en:00:00:00.000
00:01:39.725 : en:00:01:39.725
00:10:25.333 : en:00:10:25.333
00:21:56.774 : en:00:21:56.774
00:30:11.977 : en:00:30:11.977
00:43:17.178 : en:00:43:17.178
00:46:59.358 : en:00:46:59.358
00:50:39.161 : en:00:50:39.161

As you can see this file has two .srt subs included in the .mkv file and MX Player should not have any issue playing them. So what's the solution?