What's wrong with this audio amplifier and stereo to mono circuit?
The circuit is designed to operate from a positive only rail so lack of a negative rail shouldn’t be an issue.
I think your problem is the DC biasing between the VS1003 and TPA2005.
The VS1003 outputs are biased around GBUF which is about 1.2V.
The TPA2005 wants its inputs biased around VCC/2 = 2.5V.
Since these are not matched you must put AC coupling capacitors in series to block the DC component.
The TDA2005 app note shows the preferred circuit for a single ended input:

The RI in this schematic is your R25. The gain of the amp is 150K/RI so you may want to lower your value way down (from 150K) to get more gain. Make sure you change RI in both legs.
Choose RI low enough for desired gain, but CI high enough to maintain low frequency response fc at least 20Hz, as per formula in same datasheet:

If you end up using a polarized cap for CI make sure the &quot;+&quot; side faces the TDA2005, because DC level is higher on that side.