I would suggest to drop entirely VST3 presets management with any third party VST 2.x plug-in, as Sylenth1 is. It has never worked reliably for me, from which I NEVER trusted Mediabay for any presets saving with non VST3 plug-ins. When using Sylenth1 (which is VST2.4), I use only its own presets and banks management, after having saved all these in a dedicated folder, out of any possible Mediabay scan. Works perfectly and this, since more than three years.
The main problem, beside Mediabay hiccups, is : when you tweak a preset or make a new one from scratch, in which format are you going to save it ? vstpreset ? Then you no longer have up to date .fxp/.fxb files. fxp/fxb ? Then you won’t be able to use the Mediabay thingy for it. This without speaking of using both, leading to a double format/double list presets management hell…
The good answer, for me, is clearly the second one : keep on using fxp/fxb files for saving, as it allows you to have in the ‘Program selector’ of the track inspector all the presets of the last bank loaded in Sylenth1 listed, without worrying of Mediabay. With one simple bank, you have already 4 x 128 = 512 presets at disposal…