How do I reinstall letsencrypt?

I have an installation of NextcloudPI that has been running successfully for about six months. I just received a warning email from Letsencrypt that my cert is about to expire. This suprised me, since I have enabled auto-updates.
In digging through my log files, I discovered that my letsencrypt logs stopped being updated on 1/31/19. Digging further, I found in my apt log that letsencrypt had been uninstalled on that date by:

Start-Date: 2019-01-31 21:14:00
Commandline: apt-get remove -y letsencrypt

I’ve used apt and apt-get many times over the years, but I’ve never used the -y switch myself. I don’t remember explicitly removing letsencrypt. It must have happened automatically when I did and an apt update/upgrade some how.

In any case, the question is how can I recover from this? Can I just apt install letsencrypt? How can I get it to use my existing certs?

Oh yeah, pertinent details:

NextCloudPi diagnostics

NextCloudPi version  v1.9.3
NextCloudPi image    NextCloudPi_10-05-18
distribution         Raspbian GNU/Linux 9 \n \l
automount            no
USB devices          sda 
datadir              /data/ncdata
data in SD           no
data filesystem      ext2/ext3
data disk usage      7.2G/3.6T
rootfs usage         2.1G/61G
swapfile             /var/swap
dbdir                /var/lib/mysql
Nextcloud check      ok
Nextcloud version
HTTPD service        up
PHP service          up
MariaDB service      up
Redis service        up
Postfix service      up
internet check       ok
port check 80        open
port check 443       open
IP                   ***REMOVED SENSITIVE VALUE***
gateway              ***REMOVED SENSITIVE VALUE***
interface            eth0
certificates         ***REMOVED SENSITIVE VALUE***
NAT loopback         no
uptime               9days

(Sorry, I don’t know how to control the formatting)