UK Ancestry Leave to enter - out of uk for more than 180 days

I hold a UK ANCESTRY Leave to enter Visa issued October 2018. What are the implications of not meeting the 180 days in the country (over one year and or consecutive years)? I'm in my first year meeting the criteria however going into my 2nd year i need to return to SA to finish my fertility where i will stay possibly longer than 180 days due to concerns of waiting for a monitored time and assistance because of multiple miscarriages.

Will my visa be immediately canceled or is it reviewed only after the 5 years allowing me to renew from scratch stating again? I work in the uk on contract returning every 3 months to sa for 3 months but this next stay could be longer.

It is 180 days per 12 month cycle and would count backwards from potential date of ILR application.

Will my visa be immediately canceled

No.

or is it reviewed only after the 5 years allowing me to renew from scratch stating again?

You will simply need to extend for a further 5 years and pay the visa fee (currently £516) and the new doubled IHS fee (currently £2,000) again.

Note that for ILR, you require residence and proof of earnings.