To let all plates work, and preferably by their both sides, the solution is to interleave the electrodes, +-+-+-. As you probably want to separate the hydrogen from the oxygen, you need a more subtle way to collect them. Immerse the plates completely, cap them with PVC pipes cut in half? At least PVC tubes can be assembled tightly.
29V is way too much for one cell. Electrochemical cells need a minimum voltage, often 0 to 2V, that does the useful separation job. Then some voltage like 0.5V is needed to overcome the electrolyte's resistivity, but this is lost in heat and the design must minimize it. Anything over makes only unwanted reactions and more heat. It typically destroys the electrodes by badly identified side reactions and by spark-gap machining.
Do I see a metallic plate between the electrodes, possibly to keep oxygen and hydrogen separated? That won't work. You have built two electrochemical cells in series: + to separator and separator to -, with the separator working as the anode for one cell and as the cathode for the other. I believe (but may well be wrong!) that you have to design the cells and gas collectors without a gas separator.
The white foam can be the hydrogen and oxygen if they stay as bubbles long enough. Or it can be anything else due to the excessive voltage. It appears only at one side of the separators, possibly because the separator is short-circuited with the other set of electrodes.
If interleaving the electrodes, you can operate at the low voltage and with a BIG current that determines the gas production. You can compute the charge from the desired amounts (32g and 2g per mole, 22L per mole, 96500 A*s = 27 A*h per mole of electrons, H2 needs 2 electrons and O2 four): it's discouraging at tells you why industrial plants are huge and located near hydroelectric dams. It also tells why the electrodes are wide, thin and interleaved.
Putting many smaller cells in series is an other option. It won't save any power nor energy at equal gas production, but trades voltage for current and charge, which is generally useful. This is ideally done with as many tubs as cells. Or you could keep your 10 (or 11) plates in one tub but remove the conducting bolts to get 9 (or 10) cells in series; collecting separately the gases at electrodes faces won't be trivial, and stopping the current around the plates (hence between the cells) would be better. Check what voltage is reasonable for hydrogen, oxygen and stainless steel (could be 3V, I didn't check), multiply by the number of cells. 29V looks reasonable then. Batteries wouldn't last long.
You aren't far from a working setup.