Reddit mentions of PANA Brand 7oz. (Quantity: 2 Pieces) Professional Push Down Liquid Pumping Empty Bottle Dispenser (Silver Lid Clear Bottle, NO WORDING!!)

I've had this issue recently myself (same silver PLA that came with my MK3 as well after using some NGEN and then Hatchbox PLA)

Took me forever to realize the issue was my sheet. I did a nice clean wipe with Acetone and then 91% Alcohol and like magic everything I thought wasn't sticking because of Z height was actually because it wasn't adhering to the bed properly...

Also, try using the following:

Better Z Layer and Bed Calibration Test: https://www.thingiverse.com/thing:1776031

Pretty PLA v3 Config INI... These are the magic bullet settings and are a thousand times better than the shit Slic3r comes with from Prusa: https://github.com/eoprede/prusa_profiles/tree/master/MK3/Slic3r#pretty-pla-v3

Also, make sure you're using a 0.4mm Nozzle to set the Z Layer Height

Using those, get your center square perfect with Z Layer height. Then start adjusting each side with the Bed Level Calibration. It'll take a few hours but I can now print a FULL sheet first layer perfectly.

BUT FIRST AND FOREMOST, clean your sheet with Acetone and then a wipe of 91% Alcohol (or better, but AT LEAST 90%). You can get both in big bottles from Walmart for a couple bucks each. Acetone will be with the makeup as it's a nail polish remover. DO NOT overuse the Acetone. It will wear down your sheet if you scrub with it. Just do a nice wipe down using a makeup pad. Here's what I use (thanks to my wife!) though she just got me a couple from the dollar store... They are incredibly useful:

https://www.amazon.com/dp/B07CPHJSW8/ref=sspa_dk_detail_0?psc=1&pd_rd_i=B07CPHJSW8&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=21517efd-b385-405b-a405-9a37af61b5b4&pd_rd_wg=g7gbi&pf_rd_r=V23SS45VK3E88X4JZZQ2&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=P3CXg&pf_rd_i=desktop-dp-sims&pd_rd_r=52355845-df2d-11e8-a2ad-edd834b3b7f7