What has been posted is enough to be "dangerous," if it wasn't tax season I may be up for a phone call to discuss your concerns further.If you are interested in investing in a syndication and the tax treatment is a material matter I would question whether it is a good investment. 

Cost segregation looks at the $400k of the building and picks out pieces that qualify for a different treatment.

Depending on which, the treatment is entirely different. 

It does not look like there was ever any treatment done at any point to fix the issue, and some of the beams are completely rotted through.

I have a side online business, self-employed, and my CPA suggested that I should open solo 401k with that business and move my SDIRA funds into this Solo K account since it's got better tax treatment around UBIT.I contacted IRA Services and Trust (custodian) whom I have IRA account with and they said in order to open Solo K, I have to establish my company's Solo K Plan and provide them with "Self Employed 401(k) Custody Agreement".They said I can hire a CPA or lawyer to do that.

But the rest of the gain would have been due with your tax filing for tax year 2018 because you did not have receipt of those funds until 2018.b is still the appropriate treatment. 

I realize I screwed up the lease and likely made myself responsible for paying for the treatment.

Again this would only be advantageous if they intend to leave it as inheritance since the replacement property would get the same step up basis treatment and they'd get hit with huge capital gains if they sell.My firm does cost seg and it generally starts to make sense on property over $200K less land value.

Even if the tenant has a mental disability requiring treatment with an emotional support animal, it is unreasonable to expect you to suffer the consequences of dropped insurance.If you get sued, it does work in your favor that the animal was not presented to you as an Emotional Support Animal.

The man will or should be very happy  you  are willing to work with and value his renting from you....On your next lease to this man require proof of the spay and neuter and shots, rabies ect. proper flea treatment is use on the original dogs.