Missing layers?

[strange33w]

For the last few weeks I have been having issues with missing layers I think. All my print settings are the same as when my prints were coming out ok. It doesn't appear that the nozzle is having clogging issues and I cleaned and lubricated all my access rods. The printer is a craftbot plus and I have been using it for about 4 years now and this is the first time these issues have been happening. The picture below is from the start of a test print that I stopped part way through. It was printed with the default craftware PLA settings. Thank in advance for any help with resolving this.

https://imgur.com/Y9tWC4c

[airscapes]

guesses could be inexpensive PLA changing thickness causing under extrusion or slipping filament drive.