mjhjmtu

I have an Asus PCE-AC51 PCI-E WiFi card. I just freshly installed Linux Mint. The card can connect to my WiFi network, but disconnects after an indefinite amount of time (5 minutes to an hour or so). Sometimes when it disconnects, I can no longer see the network I was connected to, but I can see other networks. Sometimes I can't immediately reconnect to my network (which has a hidden SSID), but sometimes it automatically reconnects within a few seconds. The output from iwconfig is the following:

lo no wireless extensions.

wlp4s0 IEEE 802.11 ESSID:"<My SSID>" 
 Mode:Managed Frequency:5.765 GHz Access Point: 
"<My access point>" 
 Bit Rate=400 Mb/s Tx-Power=27 dBm 
 Retry short limit:7 RTS thr=2347 B Fragment thr:off
 Power Management:on
 Link Quality=70/70 Signal level=10 dBm 
 Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
 Tx excessive retries:0 Invalid misc:46 Missed beacon:0

enp3s0 no wireless extensions.

The signal level seems to oscillate between 10dBm and ~-34dBm. The output from inxi -N is the following:

Network: Card-1: Qualcomm Atheros Killer E220x Gigabit Ethernet 
Controller
 driver: alx
 Card-2: Realtek RTL8812AE 802.11ac PCIe Wireless Network 
Adapter
 driver: rtl8821ae

lshw gives the driver version as "4.15.0-20-generic".

Any suggestions, including suggestions on 5GHz wifi cards/USB wifi adapters that will work without issues in Linux, are welcome.