Tried disabling media library - removed all strings from music folder paths. Now Waveform Minibar (Mod) plugin doesn't remember waveforms, but a couple of restarts and the same situation - low Opus level, +5 dB RG scan result. And it's remarkable that every second restart shows the problem, and every other one - does not (everything seems ok then, level is normal, etc.).
Below down here is my components report.
Core (2017-11-24 08:00:06 UTC)
foobar2000 core 1.3.17
foo_abx.dll (2017-09-02 08:58:25 UTC)
ABX Comparator 2.0.4
foo_ac3.dll (2017-02-24 10:25:27 UTC)
AC3 decoder 0.9.8
foo_albumlist.dll (2017-11-24 07:58:40 UTC)
Album List 4.5
foo_asap.dll (2016-11-05 11:24:12 UTC)
ASAP 3.2.0
foo_benchmark.dll (2015-12-24 21:07:12 UTC)
Decoding Speed Test 1.2.3
foo_bpm.dll (2014-08-10 15:42:54 UTC)
BPM Analyser 0.2.4.6
foo_cdda.dll (2017-11-24 07:58:36 UTC)
CD Audio Decoder 3.0
foo_converter.dll (2017-11-24 07:58:34 UTC)
Converter 1.5
foo_convolve.dll (2015-12-24 20:29:04 UTC)
Convolver 0.3
foo_dsp_dither.dll (2017-02-23 11:17:06 UTC)
Smart Dither 1.0.4
foo_dsp_eq.dll (2017-11-24 07:58:56 UTC)
Equalizer 1.2
foo_dsp_meiercf.dll (2016-06-12 06:06:25 UTC)
Meier Crossfeed 1.1
foo_dsp_pregap.dll (2016-06-12 06:33:23 UTC)
Pregap DSP 1.0
foo_dsp_prvb.dll (2017-02-24 10:25:27 UTC)
Programmable reverb DSP 1.3
foo_dsp_resampler.dll (2012-12-08 11:07:54 UTC)
SoX Resampler 0.8.2
foo_dsp_resampler_mod.dll (2012-12-08 11:09:10 UTC)
SoX Resampler mod 0.8.2 mod
foo_dsp_skip_silence.dll (2011-06-26 12:56:22 UTC)
Skip Silence 1.0
foo_dsp_std.dll (2017-11-24 07:58:42 UTC)
Standard DSP Array 1.3.1
foo_dsp_vocal_exciter.dll (2017-02-23 11:16:55 UTC)
Vocal Exciter 1.0
foo_dsp_winamp.dll (2010-01-23 05:39:18 UTC)
Winamp DSP Bridge 1.4.7
foo_dsp_xgeq.dll (2012-02-05 09:11:00 UTC)
Graphic Equalizer 0.3.7
foo_dumb.dll (2017-10-28 18:35:46 UTC)
DUMB module decoder 2.0.2
foo_fileops.dll (2017-11-24 07:57:40 UTC)
File Operations 2.2.2
foo_freedb2.dll (2017-11-24 07:57:34 UTC)
Online Tagger 0.7
foo_gep.dll (2017-09-02 08:58:25 UTC)
Game Emu Player 1.211
foo_httpcontrol.dll (2016-04-16 11:30:24 UTC)
HTTP Control 0.97.17
foo_infospect.dll (2008-02-01 17:02:58 UTC)
Infospect 1.0.3
foo_input_adplug.dll (2017-02-24 10:25:27 UTC)
AdPlug 1.48
foo_input_avs.dll (2017-05-22 15:09:31 UTC)
AVS input 0.5
foo_input_dsdiff.dll (2017-02-24 10:25:27 UTC)
DSDIFF Decoder 1.5
foo_input_dts.dll (2017-02-24 10:25:27 UTC)
DTS decoder 0.5.3
foo_input_hvl.dll (2017-02-24 10:25:27 UTC)
Hively Tracker decoder 1.18
foo_input_kdm.dll (2017-02-24 10:25:27 UTC)
KDM Decoder 1.2
foo_input_mdx.dll (2012-02-11 19:31:54 UTC)
MDC input 1.0.1
MDX input 1.1.0
foo_input_monkey.dll (2017-12-11 19:39:22 UTC)
Monkey's Audio Decoder 2.1.9
foo_input_nsf.dll (2008-04-23 20:00:00 UTC)
NSF input 1.0.2
foo_input_qsf.dll (2017-02-24 10:25:27 UTC)
Highly Quixotic 2.0.29
foo_input_snsf9x.dll (2010-04-08 10:20:00 UTC)
SNSF decoder / snes9x-gtk r314 0.04
foo_input_std.dll (2017-11-24 08:23:10 UTC)
FFmpeg Decoders 3.2.4
Standard Input Array 1.0
foo_input_tak.dll (2015-09-10 18:31:15 UTC)
TAK Decoder 0.4.7
foo_input_usf.dll (2017-12-11 19:45:36 UTC)
LazyUSF 2.2.41
foo_input_v2m.dll (2014-08-10 15:42:55 UTC)
V2M Decoder 0.2.1
foo_input_vgmstream.dll (2017-12-13 23:05:46 UTC)
vgmstream plugin r1050-861-g037ba2e
foo_input_ym.dll (2011-03-19 08:16:42 UTC)
YM Decoder 0.3
foo_input_zxtune.dll (2017-08-07 18:29:59 UTC)
ZXTune Player 0.0.7
foo_jesus.dll (2010-09-22 22:34:00 UTC)
Autosave & Autobackup 10
foo_keep_queue.dll (2010-11-12 00:28:00 UTC)
Keep Queue 0.3.5
foo_lock.dll (2017-02-24 10:25:27 UTC)
Pause on Lock 0.6
foo_lunar2.dll (2017-02-24 10:25:27 UTC)
Lunar 2 PCM decoder 0.8
foo_masstag.dll (2011-05-15 17:55:39 UTC)
Masstagger 1.8.4
foo_midi.dll (2017-12-11 19:39:22 UTC)
MIDI Player 2.0.20
foo_nds.dll (2016-06-12 06:19:37 UTC)
No Display Standby 1.1
foo_osd.dll (2017-02-24 10:25:27 UTC)
On-Screen Display 1.74
foo_out_upnp.dll (2017-12-11 19:39:22 UTC)
UPnP MediaRenderer Output 1.0 beta 16
foo_out_wasapi.dll (2017-06-24 19:04:19 UTC)
WASAPI output support 3.3
foo_play_next.dll (2016-07-02 18:31:55 UTC)
Play Next 0.2
foo_playcount.dll (2013-02-01 08:40:46 UTC)
Playback Statistics 3.0.2
foo_playlisthistory.dll (2011-05-04 11:14:38 UTC)
Playlist History 0.1.6
foo_psf.dll (2015-09-29 17:02:10 UTC)
AOPSF 2.1.9
foo_queue_random.dll (2016-06-12 06:26:39 UTC)
Enqueue Random 0.4
foo_queuecontents.dll (2013-01-02 09:16:10 UTC)
Queue Contents Editor 0.5.1
foo_quicktag.dll (2011-05-15 17:55:44 UTC)
Quick Tagger 1.0.3
foo_rg_trn.dll (2011-05-15 17:55:45 UTC)
ReplayGain override 0.1.3
foo_rgscan.dll (2017-11-24 08:03:34 UTC)
ReplayGain Scanner 2.2.2
foo_sanitizer.dll (2017-12-11 19:45:48 UTC)
Tag Sanitizer 1.1
foo_sid.dll (2017-02-24 10:25:27 UTC)
sidplay2 1.36
foo_skip.dll (2017-09-02 08:58:25 UTC)
Skip Track 1.9.9
foo_sqlite.dll (2017-12-11 19:45:45 UTC)
SQLite Viewer 1.1.0
foo_stop_after_queue.dll (2017-09-02 08:58:25 UTC)
Stop After Queue 1.1
foo_stop_on_current.dll (2016-09-22 17:02:02 UTC)
Stop on Current 0.6
foo_stop_on_error.dll (2016-06-12 06:33:20 UTC)
Stop on Error 0.4
foo_tfsandbox.dll (2017-02-24 12:40:02 UTC)
Title Formatting Sandbox 1.0.3
foo_ui_columns.dll (2017-09-02 08:59:25 UTC)
Columns UI 0.5.1
foo_ui_std.dll (2017-11-24 07:58:50 UTC)
Default User Interface 0.9.5
foo_uie_lyrics3.dll (2016-04-16 07:45:18 UTC)
Lyric Show Panel 3 0.5
foo_uie_peakmeter.dll (2007-10-20 10:03:00 UTC)
Peakmeter Panel 0.0.4.2 beta
foo_uie_sql_tree.dll (2017-12-11 19:45:41 UTC)
SQL Tree 2.0.3
foo_unpack.dll (2017-11-24 07:58:40 UTC)
ZIP/GZIP/RAR Reader 1.8
foo_unpack_7z.dll (2017-02-24 10:25:27 UTC)
7-ZIP Reader 1.12
foo_unpack_jma.dll (2010-01-13 14:52:08 UTC)
JMA reader 1.3
foo_unpack_lha.dll (2017-02-24 10:25:27 UTC)
LHA reader 1.13
foo_unpack_unix.dll (2017-02-24 10:25:27 UTC)
Unix archive reader 1.10
foo_verifier.dll (2017-12-11 19:39:22 UTC)
File Integrity Verifier 1.2.1
foo_vis_oscilloscope_d2d.dll (2017-02-24 12:40:09 UTC)
Oscilloscope (Direct2D) 1.1.0
foo_vis_shpeck.dll (2009-09-28 07:32:16 UTC)
Shpeck - Winamp vis plugins wrapper 0.3.7
foo_vst.dll (2011-03-05 04:19:00 UTC)
VST 2.4 adapter 0.9.0.3
foo_wave_minibar_mod.dll (2017-12-11 19:20:17 UTC)
Waveform Minibar (mod) 1.0.3
foo_whatsnew.dll (2017-02-25 10:55:34 UTC)
Feature Watcher 1.1.1