VPN throttling over mobile?

[wn78]

I've had connection problems with VPN over mobile hotspots on my last trip.  

I would pop a TRUE SIM (prepaid) into my phone, turn on the hotspot, connect my laptop to it, and use ExpressVPN on the laptop.  I noticed lagging connections with video calls and remote desktop sessions, anything that requires a steady connection was freezing up.  I ran a ping/traceroute, and saw latency spikes, constant packet drops, and the connection going dead for a few seconds every minute or so.  Disconnected the VPN and the connection becomes steady.  Thinking maybe it’s the VPN server, I tried many different VPN servers in the USA and different VPN protocols, it would improve for a short time, but then interruptions restart.  Then, keeping the same VPN server I switched my phone to an AIS SIM card and the connection immediately became steady, so I figured it was not the VPN problem, but TRUE.  Everything was smooth for a few days on AIS, but then started having the same interruptions on AIS.  Same issues with a DTAC SIM later.  I started to suspect all of them were detecting VPN and throttling it.  I've used VPN for years on my travels to Thailand and have not had such issues until the last trip.  

Anyone has similar experiences with a VPN over hotspots lately?
 

Edited April 12 by wn78