Hi

I do have empathy with you over this issue as I have extended family there; my departed father's wife. I was allowed to visit whilst on bail back in 2011 but after my conviction (buying sexual services) I have always been told I would not be allowed back in.

Hopefully a successful outcome for you will arise for you.

Learn from yesterday, live for today, hope is for tomorrow else what is left if you remove a mans hope.

Thank you for this information.

Thailand has had a crack-down on people potentially traveling to the country for illicit purposes. I'm fairly sure that during your last visit they were less firm and let you in. Details of your offence has clearly been kept on their file hence not being allowed in now. I have had a look at Thailand's visa rules and from what I can understand (and I am sure someone will correct me if I am wrong) you would need to apply for a visa through their electronic system at https://www.thaievisa.go.th/ ahead of travel and not rely on their visa-free option. If the e-system grants you a visa I can't see why they would stop you at the border.And if you are rejected, hopefully it would give you potential next steps.

I had a SHPO and on SOR from 2015 to 2020. (from age 55 to 60. I'm 63 now)
During 2016 my Thai gf (who i met after my offence and i did tell her all about it) wanted us to visit her country. 
I arranged return flights etc, informed the police 7 days before travel and we went.  Upon entering the country there were no problems but on leaving the passport officer spotted a message on my details that led to me being held up whilst they decided what to do. They eventually let me leave.
I thought no more about it but we decided not to return there until after 2020.
our relationship blossomed and I proposed to my future wife last year. We have been making plans to possibly retire to Thailand in the future. My fiance went  to Thailand in Oct '23 to project manage a house build for our future there. I was due to fly out in late Jan '24 (landing in Chiang Mai) and be with her for the final 3 weeks. Then we return to the UK together.
Upon arrival at Chiang Mai I was not allowed to enter the country. Immigration control read my details and after long discussions with what seemed like the whole force they instructed me I could not enter and to buy a return ticket on the first available flight home. Understandably I was very upset and managed to get word to my fiance who had been waiting to meet me outside. We were both very upset about the whole episode. 
My fiance did all she could whilst I was held there, She pleaded my case to immigration but all in vain.
when i returned to UK I went straight to the police station to ask VISOR team about the 'restriction'. They got back to me and said there was no restriction or information held on me to stop me moving around the world, it ceased in 2020.
My next stop was the Royal Thai Embassy in London. They were unable to even look at my passport details and were a waste of time but at least I ticked that off my list also.
Meanwhile my fiance had got in touch with the immigration office in Chiang Mai. I emailed her all my details (copies of my conviction, passport, 'spent' letter etc.) I also emailed the same documents to the office she was due to visit.  It was all in vain again because they only directed her to the Immigration Office Division 3 in Bangkok. So I sent them all the same details, My fiance flew down there overnight and met them in the morning. They then asked her to "TRANSLATE" all the English into Thai. It took her a few hours but she did it all and returned to them. They agreed to look at my case and let us know their decision in two to three weeks. 
So now here I am siting at home for the last week and a half feeling very sad and lonely wondering what will be the outcome. I am very worried that they might never grant me permission to enter Thailand and all our future plans together might go awry.  Obviously we hope for the best outcome but after reading stuff on the internet I am very worried still. Does anyone here reading this have any advice for me and is there another path I can go down ( lawyers and such like) if I don't get permission from this application? Thank you for reading.