VPN works on Wi-Fi but not on mobile data: causes and fixes
Connects at home but fails on 4G or 5G? How carriers treat UDP, protocols and background data, and what to check on your phone, step by step.
Same phone, same app, same server: at home on Wi-Fi the VPN connects in seconds, but on 4G or 5G it spins and gives up, or connects and carries nothing. Because only the network changed, the cause is almost always in the mobile network itself or in how your phone treats mobile data. This guide goes through both.
Rule out the phone first
These settings block an app on mobile data only, so they are easy to miss.
- Mobile data without the VPN. Disconnect the VPN, turn Wi-Fi off and open a website. If it does not load, the problem is your tariff, coverage or the operator, not the VPN.
- Mobile data allowed for Colitu. On Android open Settings → Apps → Colitu → Mobile data (the name varies by maker) and allow both foreground and background data. Some makers' firmware also has a separate per-app network permission that can block mobile data for one app. On iPhone check Settings → Mobile Service (Cellular) and make sure Colitu is allowed.
- Data Saver. Android's Data Saver restricts background data for most apps. Turn it off, or add Colitu to the apps with unrestricted data.
- Roaming. Abroad, data roaming must be on, and some partner networks restrict traffic more than at home.
- Date and time. Set them to automatic. A wrong clock breaks TLS on any network, but people often notice it first on mobile.
Why mobile networks behave differently
UDP and QUIC are treated differently. Most fixed-line providers pass UDP without fuss. Some mobile operators throttle UDP, limit QUIC or block it outright. Hysteria2, the fastest Colitu protocol, runs over QUIC, that is over UDP, so it is the first to suffer. Our guide on UDP blocking explains this in detail.
Carrier-grade NAT. Operators usually put many subscribers behind one public address (CGNAT). The NAT keeps a short-lived mapping for every flow, and UDP mappings can expire sooner than on a home router. An idle UDP connection can then quietly stop working until it is set up again.
Different filtering. Traffic filtering on mobile networks may be stricter than on home internet, or simply configured differently. A protocol that passes on your home provider may be recognised and slowed down on the mobile network.
Regional restrictions. In some regions, mobile internet is at times limited to a short list of approved services. In that case the VPN server is simply unreachable over mobile data and no protocol can help; Wi-Fi or a fixed line may still work.
Weak signal. At the edge of coverage packets get lost. TCP-based protocols slow down sharply under loss, while Hysteria2 is designed to keep its pace, provided UDP gets through.
What Colitu does automatically
You do not choose the protocol in Colitu: Adaptive Connect does it for you. On Android and iOS it tries the transports in this order: Hysteria2, VLESS Reality, VLESS XHTTP, Trojan, Shadowsocks 2022. Each one is kept only when real traffic passes a check, which takes up to about 12 seconds on Android and about 9 seconds on iOS. A transport that carried nothing is pushed back, and Android remembers the last working transport for each server, so the next connection to that server starts with what worked last time.
In practice this means that on a difficult mobile network the first connection can take noticeably longer than on Wi-Fi. Give the app time and do not keep tapping Connect.
Step by step on the phone
- Turn Wi-Fi off so the phone does not keep switching between networks.
- Switch airplane mode on for ten seconds and off again: the operator gives you a fresh connection.
- Open Colitu, connect and wait until it reports the result.
- If it fails, choose another location in the server list and try again.
- Restart the phone if the app connected earlier today on mobile data but no longer does.
- Check whether the problem follows the SIM card: if a friend's SIM from another operator works in your phone, the cause is your operator's network.
When the VPN connects but nothing loads
If the app shows Connected on mobile data but pages do not open, see VPN connected but no internet. On mobile data the usual reasons are a lost connection after moving between cells or from Wi-Fi, and Android's Block connections without VPN holding traffic while the VPN reconnects.
What not to do
- Do not run a second VPN or a "traffic booster" at the same time: only one VPN can be active on a device.
- Do not disable the kill switch to get online; fix the tunnel instead.
- Do not reset the phone to factory settings because of this problem: it almost never helps with an operator-side restriction.
Quick reference
| Symptom | Likely cause | What to try |
|---|---|---|
| No internet on mobile data even without VPN | Tariff, coverage or operator | Contact the operator |
| VPN fails only on mobile data | UDP or protocol restricted | Wait for fallback, change location |
| Works on one SIM but not another | Operator network | Use Wi-Fi, contact support |
| Connects and drops when you move | Network change, CGNAT | Reconnect, check battery settings |
| Never reachable on mobile data in an area | Regional restriction | Use Wi-Fi or a fixed line |
If nothing helps, write to support from the support page and include your operator, region and app version. The help centre has more connection checks and an Android guide.