Well I use Fireband's "default" profile for SNES 256, I didn't touch it:
{
"version": "0.86",
"main": [
{
"profile_name": "SNES 256",
"video_lpf": "9MHz (SDTV)",
"ypbpr_cs": "Rec. 601",
"r_f_off": "128",
"g_f_off": "128",
"b_f_off": "128",
"r_f_gain": "26",
"g_f_gain": "26",
"b_f_gain": "26",
"c_gain": "8",
"clamp_offset": "128",
"alc_v_filter": "10",
"alc_h_filter": "3",
"s480p_mode": "Auto",
"s400p_mode": "VGA 640x400@70",
"tvp_hpll2x": "On",
"upsample2x": "Off",
"sync_lpf": "2.5MHz (max)",
"stc_lpf": "4.8MHz (HDTV/PC)",
"sync_vth": "11",
"linelen_tol": "6",
"vsync_thold": "68",
"pre_coast": "1 lines",
"post_coast": "0 lines",
"pm_240p": "Line4x",
"pm_384p": "Line2x",
"pm_480i": "Line4x (bob)",
"pm_480p": "Line2x",
"pm_1080i": "Passthru",
"l2_mode": "256x240 optim.",
"l3_mode": "256x240 optim.",
"l4_mode": "256x240 optim.",
"l5_mode": "256x240 optim.",
"l5_fmt": "1920x1080",
"ar_256col": "8:7",
"tx_mode": "HDMI (RGB)",
"hdmi_itc": "Off",
"sl_mode": "Off",
"sl_str": "0",
"sl_hybr_str": "0",
"sl_method": "Multiplication",
"sl_altern": "On",
"sl_id": "Top",
"sl_altiv": "Off",
"sl_type": "Horizontal",
"sl_cust_l_str_1": "0",
"sl_cust_l_str_2": "0",
"sl_cust_l_str_3": "0",
"sl_cust_l_str_4": "0",
"sl_cust_l_str_5": "0",
"sl_cust_c_str_1": "0",
"sl_cust_c_str_2": "0",
"sl_cust_c_str_3": "0",
"sl_cust_c_str_4": "0",
"sl_cust_c_str_5": "0",
"sl_cust_c_str_6": "0",
"h_mask": "0",
"v_mask": "8",
"mask_color": "Black",
"mask_br": "0",
"reverse_lpf": "0",
"full_tx_setup": "Off",
"vga_ilace_fix": "Off",
"av3_alt_rgb": "Off",
"panasonic_hack": "Off",
"default_vic": "0",
"audio_dw_sampl": "2x (fs = 48kHz)",
"audio_swap_lr": "Off",
"audio_gain": "12",
"link_av": "No link",
"export_enabled": "true"
}
],
"timing_tweaker": [
[
{
"name": "512x240",
"h_active": "512",
"v_active": "240",
"h_total": "682",
"h_total_adj": "0",
"h_backporch": "75",
"v_backporch": "15",
"h_synclen": "50",
"v_synclen": "3",
"sampler_phase": "22"
},
{
"name": "384x240",
"h_active": "384",
"v_active": "240",
"h_total": "487",
"h_total_adj": "17",
"h_backporch": "41",
"v_backporch": "14",
"h_synclen": "37",
"v_synclen": "3",
"sampler_phase": "23"
},
{
"name": "320x240",
"h_active": "320",
"v_active": "240",
"h_total": "427",
"h_total_adj": "0",
"h_backporch": "49",
"v_backporch": "15",
"h_synclen": "31",
"v_synclen": "3",
"sampler_phase": "16"
},
{
"name": "256x240",
"h_active": "256",
"v_active": "240",
"h_total": "341",
"h_total_adj": "0",
"h_backporch": "38",
"v_backporch": "15",
"h_synclen": "25",
"v_synclen": "3",
"sampler_phase": "22"
},
{
"name": "480i",
"h_active": "704",
"v_active": "240",
"h_total": "910",
"h_total_adj": "0",
"h_backporch": "98",
"v_backporch": "15",
"h_synclen": "62",
"v_synclen": "3",
"sampler_phase": "2"
},
{
"name": "480p",
"h_active": "720",
"v_active": "480",
"h_total": "858",
"h_total_adj": "0",
"h_backporch": "59",
"v_backporch": "30",
"h_synclen": "62",
"v_synclen": "6",
"sampler_phase": "6"
}
]
]
}
And you are rigt I think, it drops sync because red LED on OSSC goes on during this drops. But I don't experience this on and other game so far, that is strange to me.