We not have trips to HCMC, but from customer we hear following: if you can proof bank statement three month, good enough skills than HCMC is OK. Penang, Kota Bharu even Yangon too. Vientiane is OK, but they observe the one full year rule. Savannakhet no. Did not hear anything from Phnom Penh (best avoided anyway). KL & Hanoi is a no go for ED (IMHO).
I never understood why a huge number of people switched and went to HCMC. If your intention is study and your documents are OK than other places are more welcoming.
as Robert said : the Mukdahan/Savannakhet border is easy. As you allowed TWO entries under visa exempt in one calendar year you should be OK doing a border run there.
I can not give a solution, but the visa history pretty much is the explanation for denial. All places are critical with ED applications, especially from informal schools. Why not sign up at a real College? OP also did not explain if he got VOID stamp and just refuse to accept his application.
a border run would solve the gap. You allowed two in one year. Depending of where you stay a border is never far away. Just avoid Poi Pet. Than back in US you can apply for a Non O.
, no, they not stamp Russian, even with multiple entry, they say Myanmar side not OK. Again this might only be a rule at Kanchanaburi, other border might be OK.