Real Estate market is similar to other market, which is unpredictable, nobody can predict the future clearly, And it is tied to other market to, positively or negatively.So the overall market may go up 20% next year, but here is where you need to distinguish be smart and being lucky.

You have a maintenance issue…unpredictable cash flow.

I keep receiving mails from  insurance and mortgage companies to protect my home by getting a mortgage insurance. life is unpredictable and this seems like a no brainer.

CAPEX doesn't occur on a predictable schedule.What I have observed over time is that CAPEX is unpredictable.

(Fortunately, we were insured)Emergency Fund: Always have extra cash for unexpected events.Tenant Support: Keep good communication and support your tenants through tough times.Final ThoughtsThis July 4th was a disaster, but it’s also a stark reminder of the unpredictable nature of real estate investing.

It's also less passive and unpredictable than a LTR. 

I also doubt it would impact appraised value but those are a bit more unpredictable.

But I couldn't tell you how many times I was frustrated, heartbroken,  upset, and nervous, because I had higher/unrealistic expectations set and was not prepared to weather the challenges, which were unpredictable to me.

Perhaps instead consider using private money, doing the reno as quickly as possible, and then using a DSCR or conventional refi to pay off the private money.I tend to agree with @Drew Sygit and @Nathan Gesner that tapping the equity of your primary, especially with something variable and unpredictable like a HELOC, is not a good idea, but with one exception.

In 2010-2016ish buying was easy, selling took half a year with unpredictable outcome.