Network/download stops every few seconds for any amount of time

I am using Ubuntu 20.04.3 LTS. For every download since the last few days, the download just stops. For any amount of duration. I have used USB tethering or mobile hotspot with the same results. Speed test shows I am getting 13mbps but the problem persists. I suspect something to do with software and not ISP. So far I have run continuous ping every 30 seconds to google, every 15 minutes speed test. My ISP is bad many times but it's not so bad that it would take an hour or two to download a 1.5 MB file, with intermittent drops of unknown duration.

What tests should I run to dig deeper?

Thanks in advance!

Update 1

Two experiments:

1. Kept on seeing messages about org.freedesktop.Tracker1 (in /var/log/syslog as suggested by @matigo in comments). Disabled it as per tracker service running every minute

2. Yesterday, when I switched from wireless (mobile hotspot) to USB tethering, had much better experience. Problem with USB tethering is, my ISP's sweet spot cannot be used even if I move phone even couple of meters so network speed drops considerably (from 13 mbps to ~3 mbps)

3. output of sudo journalctl -b 0 -u NetworkManager although this is with USB tethering as suggested by @waltinator (reading man page pending)

    Jan 19 08:58:50 my-machine systemd[1]: Starting Network Manager...
    Jan 19 08:58:58 my-machine NetworkManager[903]: <info>  [1642562938.9848] NetworkManager (version 1.22.10) is starting... (for the first time)
    Jan 19 08:58:58 my-machine NetworkManager[903]: <info>  [1642562938.9849] Read config: /etc/NetworkManager/NetworkManager.conf (lib: 10-dns-res>
    Jan 19 08:59:00 my-machine NetworkManager[903]: <info>  [1642562940.6347] bus-manager: acquired D-Bus service "org.freedesktop.NetworkManager"
    Jan 19 08:59:00 my-machine systemd[1]: Started Network Manager.
    Jan 19 08:59:01 my-machine NetworkManager[903]: <info>  [1642562941.7495] manager[0x55f6bc7c0010]: monitoring kernel firmware directory '/lib/f>
    Jan 19 08:59:01 my-machine NetworkManager[903]: <info>  [1642562941.7496] monitoring ifupdown state file '/run/network/ifstate'.
    Jan 19 08:59:02 my-machine NetworkManager[903]: <info>  [1642562942.2371] hostname: hostname: using hostnamed
    Jan 19 08:59:02 my-machine NetworkManager[903]: <info>  [1642562942.2371] hostname: hostname changed from (none) to "my-machine"
    Jan 19 08:59:02 my-machine NetworkManager[903]: <info>  [1642562942.2376] dns-mgr[0x55f6bc79e290]: init: dns=systemd-resolved rc-manager=symlin>
    Jan 19 08:59:02 my-machine NetworkManager[903]: <info>  [1642562942.2391] rfkill2: found Wi-Fi radio killswitch (at /sys/devices/pci0000:00/000>
    Jan 19 08:59:02 my-machine NetworkManager[903]: <info>  [1642562942.2394] rfkill0: found Wi-Fi radio killswitch (at /sys/devices/platform/acer->
    Jan 19 08:59:02 my-machine NetworkManager[903]: <info>  [1642562942.2526] manager[0x55f6bc7c0010]: rfkill: Wi-Fi hardware radio set enabled
    Jan 19 08:59:02 my-machine NetworkManager[903]: <info>  [1642562942.2526] manager[0x55f6bc7c0010]: rfkill: WWAN hardware radio set enabled
    Jan 19 08:59:03 my-machine NetworkManager[903]: <info>  [1642562943.3988] Loaded device plugin: NMWifiFactory (/usr/lib/x86_64-linux-gnu/Networ>
    Jan 19 08:59:04 my-machine NetworkManager[903]: <info>  [1642562944.5808] Loaded device plugin: NMBluezManager (/usr/lib/x86_64-linux-gnu/Netwo>
    Jan 19 08:59:04 my-machine NetworkManager[903]: <info>  [1642562944.6957] Loaded device plugin: NMTeamFactory (/usr/lib/x86_64-linux-gnu/Networ>
    Jan 19 08:59:04 my-machine NetworkManager[903]: <info>  [1642562944.7319] Loaded device plugin: NMWwanFactory (/usr/lib/x86_64-linux-gnu/Networ>
    Jan 19 08:59:05 my-machine NetworkManager[903]: <info>  [1642562945.3128] Loaded device plugin: NMAtmManager (/usr/lib/x86_64-linux-gnu/Network>
    Jan 19 08:59:05 my-machine NetworkManager[903]: <info>  [1642562945.3134] manager: rfkill: Wi-Fi enabled by radio killswitch; enabled by state >
    Jan 19 08:59:05 my-machine NetworkManager[903]: <info>  [1642562945.3136] manager: rfkill: WWAN enabled by radio killswitch; enabled by state f>
    Jan 19 08:59:05 my-machine NetworkManager[903]: <info>  [1642562945.3137] manager: Networking is enabled by state file
    Jan 19 08:59:05 my-machine NetworkManager[903]: <info>  [1642562945.3139] dhcp-init: Using DHCP client 'internal'
    Jan 19 08:59:07 my-machine NetworkManager[903]: <info>  [1642562947.4575] settings: Loaded settings plugin: ifupdown ("/usr/lib/x86_64-linux-gn>
    Jan 19 08:59:07 my-machine NetworkManager[903]: <info>  [1642562947.4576] settings: Loaded settings plugin: keyfile (internal)
    Jan 19 08:59:07 my-machine NetworkManager[903]: <info>  [1642562947.4576] ifupdown: management mode: unmanaged
    Jan 19 08:59:07 my-machine NetworkManager[903]: <warn>  [1642562947.5149] ifupdown: interfaces file /etc/network/interfaces doesn't exist
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.1363] device (lo): carrier: link connected
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.1368] manager: (lo): new Generic device (/org/freedesktop/NetworkManager/De>
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.1401] manager: (enp5s0): new Ethernet device (/org/freedesktop/NetworkManag>
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.1437] device (enp5s0): state change: unmanaged -> unavailable (reason 'mana>
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.1706] manager: (wlp4s0): new 802.11 Wi-Fi device (/org/freedesktop/NetworkM>
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.1724] device (wlp4s0): state change: unmanaged -> unavailable (reason 'mana>
    Jan 19 08:59:09 my-machine NetworkManager[903]: <warn>  [1642562949.4101] Error: failed to open /run/network/ifstate
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.7044] supplicant: wpa_supplicant running
    Jan 19 08:59:09 my-machine NetworkManager[903]: <info>  [1642562949.7053] device (wlp4s0): supplicant interface state: init -> starting
   

update 2

Is it possible that this problem persists because route tables at ISP's end are messed up? Please see below for example: